A Newcastle University study involving thousands of families is helping prospective parents work out whether they are likely to have sons or daughters. Show
The work by Corry Gellatly, a research scientist at the university, has shown that men inherit a tendency to have more sons or more daughters from their parents. This means that a man with many brothers is more likely to have sons, while a man with many sisters is more likely to have daughters. The research involved a study of 927 family trees containing information on 556,387 people from North America and Europe going back to 1600. "The family tree study showed that whether you’re likely to have a boy or a girl is inherited. We now know that men are more likely to have sons if they have more brothers but are more likely to have daughters if they have more sisters. However, in women, you just can’t predict it," Mr Gellatly explains. Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother’s X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother’s to make a boy (XY). The Newcastle University study suggests that an as-yet undiscovered gene controls whether a man’s sperm contains more X or more Y chromosomes, which affects the sex of his children. On a larger scale, the number of men with more X sperm compared to the number of men with more Y sperm affects the sex ratio of children born each year. Sons or daughters? A gene consists of two parts, known as alleles, one inherited from each parent. In his paper, Mr Gellatly demonstrates that it is likely men carry two different types of allele, which results in three possible combinations in a gene that controls the ratio of X and Y sperm;
“The gene that is passed on from both parents, which causes some men to have more sons and some to have more daughters, may explain why we see the number of men and women roughly balanced in a population. If there are too many males in the population, for example, females will more easily find a mate, so men who have more daughters will pass on more of their genes, causing more females to be born in later generations,” says Newcastle University researcher Mr Gellatly. More boys born after the wars In many of the countries that fought in the World Wars, there was a sudden increase in the number of boys born afterwards. The year after World War I ended, an extra two boys were born for every 100 girls in the UK, compared to the year before the war started. The gene, which Mr Gellatly has described in his research, could explain why this happened. As the odds were in favour of men with more sons seeing a son return from the war, those sons were more likely to father boys themselves because they inherited that tendency from their fathers. In contrast, men with more daughters may have lost their only sons in the war and those sons would have been more likely to father girls. This would explain why the men that survived the war were more likely to have male children, which resulted in the boy-baby boom. In most countries, for as long as records have been kept, more boys than girls have been born. In the UK and US, for example, there are currently about 105 males born for every 100 females. It is well-documented that more males die in childhood and before they are old enough to have children. So in the same way that the gene may cause more boys to be born after wars, it may also cause more boys to be born each year. How does the gene work? The trees (above) illustrate how the gene works. It is a simplified example, in which men either have only sons, only daughters, or equal numbers of each, though in reality it is less clear cut. It shows that although the gene has no effect in females, they also carry the gene and pass it to their children. In the first family tree (A) the grandfather is mm, so all his children are male. He only passes on the m allele, so his children are more likely to have the mm combination of alleles themselves. As a result, those sons may also have only sons (as shown). The grandsons have the mf combination of alleles, because they inherited an m from their father and an f from their mother. As a result, they have an equal number of sons and daughters (the great grandchildren). In the second tree (B) the grandfather is ff, so all his children are female, they have the ff combination of alleles because their father and mother were both ff. One of the female children has her own children with a male who has the mm combination of alleles. That male determines the sex of the children, so the grandchildren are all male. The grandsons have the mf combination of alleles, because they inherited an m from their father and f from their mother. As a result, they have an equal number of sons and daughters (the great-grandchildren).
Story Source: Materials provided by Newcastle University. Note: Content may be edited for style and length.
Published on November 2nd, 2020 and Updated on February 15th, 2022 Check out SneakPeek Traits Test to find out what your baby will look like as an adult! Speculating about how your future kiddo will turn out can be a fun little game. It’s hard not to make guesses and predictions about which traits she’ll inherit from you and your partner respectively, and it seems even harder for friends and family not to put in their two cents (or two dollars). A traits DNA test can help remove the guessing game and get you even more excited about your little one’s arrival. Maybe your mother-in-law is convinced your daughter is destined for the signature family nose. Meanwhile, your best friends keep telling you that your baby girl is going to inherit your killer smile. Maybe your dad is convinced all future children will inherit his love of sports (he may already be stockpiling tiny jerseys). So what’s the truth, and what’s an old wives’ (or husbands’) tale when it comes to traits inherited from the dad? Genetics of InheritanceMost genetic traits result from a combination of both parents’ genetic codes. A dash of mom, a sprinkle of dad, mix it all together, bake for nine months, and voila: you have a darling little bun, fresh out the oven. You may be wondering, “where does the hair gene come from” or “what color eyes will my baby have?” and we can help narrow the guessing game down for you! But when it comes to tracing certain traits to certain parents, scientists have identified a particular type of gene responsible for parent-specific traits: Sex-Linked GenesWhile moms pass down an X chromosome to their children—since women have two x chromosomes—dads pass down either an X or Y chromosome. The presence of a Y chromosome determines whether your baby’s a boy or a girl. Additionally, certain genetic traits are found exclusively on X or Y chromosomes. And since fathers are the only ones who can contribute a Y chromosome, Y-linked traits are all thanks to the baby’s father. What do you inherit from your father?Now that we’ve covered a brief overview of genetics, let’s dive into the good stuff. What are the physical traits inherited from father? #1 Baby’s GenderDads are responsible for the gender of their little rugrats, and it’s one of the physical traits that are 100% contributed by dad. The Supporting Evidence: While mothers will always pass down their X chromosome (considering it’s the only kind they have), fathers will pass down either an X or Y chromosome at random. The gendered difference is entirely dependent on this one minuscule genetic distinction:
The Big Picture: All of the physical differences between boys and girls are due to this tiny chromosomal difference. Dad’s contribution makes a big impact and can significantly affect the different traits your little one will have! #2 Y-Linked Traits (for Sons)Sons can only inherit a Y chromosome from dad, which means all traits that are only found on the Y chromosome come from dad, not mom. Background: All men inherit a Y chromosome from their father, and all fathers pass down a Y chromosome to their sons. Because of this, Y-linked traits follow a clear paternal lineage. A mutation on the Y chromosome can only be passed from father to son, and all mutations are considered “dominant” in that there’s no second Y chromosome from mom to alter or mitigate the effects. In addition to the male traits of sperm development, hormone levels, and other distinctly male physical characteristics, there are other non-gendered Y-linked traits:
The Big Picture: Relatives and friends might tell your son he looks identical to his father, and your partner may even feel pride in saying, “like father, like son” when your son does something adorable. For the most part, there’s no real indication that boys take after their dads in looks any more than they look like mom, but Y-linked traits are the exception to this rule. #3 HeightAt least 700 genetic variations are responsible for determining height, coming from both mom and dad’s genes. But there is evidence to suggest that each parent’s “height gene” functions a bit differently. Dad’s genes play a significant role in promoting growth. The Supporting Evidence: The insulin-like growth factor (IGF protein) is strongly expressed by paternal genes. This genetic trait is also responsible for promoting growth. However, mom’s genes express a somewhat contradictory receptor called IGF2R, which essentially does the opposite by actively repressing dad’s height-inducing genes. These are both examples of genomically imprinted genes. The imprinted gene is stamped by the origin parent from the beginning, distinctly marking mom’s copy and dad’s copy of the allele. The stamped gene and inherited trait are expressed differently depending on which parent they came from, or they’re only expressed when inherited from one parent, not the other. It doesn’t matter if Mom’s an Amazon when it comes to height or if Dad’s height is better suited for soccer rather than basketball—Dad’s IGF genes encourage the child to grow tall, while Mom’s IGF2R genes say, slow down buddy, don’t leave me in the dust. In a sense, they cancel each other out, but both genes play a vital role in the growth of your offspring. Studies on mice illustrate this delicate balance between each parent’s genes:
The theories behind why this happens are fascinating from an evolutionary standpoint. These genetic differences between mom and dad are called “parent-of-origin effects” and have an impact on growth and nutrition:
The Big Picture: Beyond the give-and-take of these two specific genetic expressions, there are loads more variants affecting height from both mom and dad. Dad’s genes strongly influence your child’s size in a certain sense, but whether your children grow up to be 6’5” basketball stars or 5’10” point guards are up to certain genetic conditions from both parents. #4 X-Linked Traits (for Daughters)As we’ve learned, dads contribute one Y or one X chromosome to their offspring. Girls get two X chromosomes, one from Mom and one from Dad. This means that your daughter will inherit X-linked genes from her father as well as her mother. When your daughter inevitably ends up with his X chromosome, does that mean she’ll inherit all of his X-linked genes and traits? Genes, yes. Traits, not necessarily. The Supporting Evidence: When it comes to a trait passed from father to daughter, dad has a 100% chance of passing down any mutations or variations on his X chromosome. However, this doesn’t automatically mean that all of these mutations will present physically. Remember, girls inherit two X chromosomes—one from mom, one from dad. So while dad is passing down everything on his X chromosome, mom is also giving their daughter a second copy. Here’s where the dominant and recessive gene come into play:
Some examples include:
The Big Picture: While X-linked recessive traits are a toss-up between mom and dad’s DNA, X-linked dominant features (when the mutation is present in the father) will make their way into your little girl’s life. Put the Rumors to Rest with SneakPeek TraitsWhile you and your gal pals are pouring over family photo albums and going down the Google-search-rabbit-hole of which genes dictate your baby’s physical traits (the same Google search that—no doubt—lead you to this very article), your kiddo’s father and his buddies might be out doing the same thing. While you both might wind up making a few lucky guesses, the only real way to determine how everything shakes out is with a DNA test. SneakPeek Traits is a quick, easy-to-use DNA test to help you in answering the questions like “when do babies get freckles?” or just plain and simple “How will my baby look?” or you can even check the nutrition of your child using a DNA nutrition test. You can collect the sample from the comfort of your own home and, after sending it off to SneakPeek Labs in the included prepaid envelope, you’ll receive tons of exciting information about your baby’s traits, including:
You might even find out whether they become captain of the varsity basketball team! Oh, wait… Sorry, that’s one for the have-to-wait-and-see list. Some things about your child’s future are meant to remain a mystery—for everything else, there’s SneakPeek Traits. This post has been reviewed for accuracy by the following medical professional:
Katie Phillips, MSN, CNM, APRN Nurse midwife and mom to 5 kiddos ranging in age from 7-20 and a chocolate lab. I own my own birthing center, which is the first and only one in Bay County, Florida. I love the beach, swimming, horseback riding, and reading. Sources: |
Do males get X chromosome from mom or dad?
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