Offspring inherit information from their parents but do not look exactly like them-- why not??
Because of genetic variation. There are two important events during Meiosis that contribute to genetic variation. The first is Crossing Over. This occurs during prophase I of Meiosis and is where homologous chromosomes line up next to each other and "swap" genetic information. That will result in gametes different than the ones that made the parent because already, genetic information is swapped around. The other event is independent assortment. This ALSO results in genetic variation since it is highly unlikely that chromosomes will move to the opposite poles in the same fashion that it did in the parent. These two events create gametes that are very different from the parents. In addition to that, it's happening in BOTH parents; the mom and the dad. And when these two unique gametes combine to form the offspring, we end up with something totally new and unique.
Why do offspring of the same parents look different?
Our traits are random from our parents. They may have a dominant gen, but they giv you the recessive gene so you get the look of that recessive gene and have that look. Also, you get aleles from both parent so that helps in differentiation. The genes we recieve come in randomely so that is why we dont look like our siblings
Under What conditions would two offspring have the same genotype and phenotype?
Genotype is the combination of allelles, either dominant or recessive. Phenotype is what trait is expressed (such as tall, short, etc.) Any time two children are born and they have the save parents, they have the same probabilities of having the same genotypes and phenotypes. For example: If the mother is AA and the Father is Aa for tallness, where tallness is dominant, there is a 50% chance that the child will be AA genotype and tall (phenotype) and 50% chance that the child will be Aa (genotype) and tall (phenotype). If these children are born at different times, then they run these odds of being born with the same genotypes/phenotypes. If these children are born at the same time, but are fraternal twins, then they have the same odds as if they were born at different times. If these children are born at the same time, but are identical twins, then they would have a 100% chance of having the same genotype and phenotype. This scenario holds true regardless of the genotypes of the parents, the only thing that changes are the percentages. Each birth (separate and/or fraternal) is like the tossing of a coin....the odds are the same on each toss. Identical twins will always be 100% genotype/phenotype identical because they are the result of one egg and one sperm. BIOLOGY TEACHER
Why don't offsprings look exactly like their parents?
Children never look exactly like one parent because they are not clones of either parent. You get one copy of every gene from each parent, these copies are called alleles. Your physical appearance is determined by the interplay between the products of these alleles. For simple characteristics (those determined by only one gene) sometimes the allele from one parent produces a characteristic (we call this a phenotype) that is dominant to the characteristic produced by the other parent's allele. In this case, the child will have the same characteristic as one parent. However, in most cases, visible characteristics are determined by the interplay between products of dozens or even hundreds of genes. Layer on top of that the effects of the environment (aka even the exact same allele combination will produce different phenotypes in different environments).This is why even when children look similar to one parent in certain aspects they are not identical. For example, you and your child may both have green eyes but when you look closely the iris patterns are not identical and the color is slightly different.In equation formatcharacteristic = alleles from parent 1 + alleles from parent 2 + environment
Why are siblings different than each other when...?
Gametes are reproductive cells that are contributed by each parent to create offspring. Only one gamete from each parent makes up the cell that multiplies and becomes their offspring. Gametes have 23 chromosomes and body cells have 46 so they can be mixed and matched in many different ways. The sex chromosomes for example are always an X from a female parent and may be a X or a Y from a male parent. The result is that parents produce a boy or a girl as male body cells are XY and female body cells are XX. Similarly it is with other pairs of chromosomes. One of the distinguishing factors is that the parent randomly contributes either chromosome to a gamete and then randomly that gamete combines with the gamete from the other parent of the opposite gender making ultimately a myriad variations possible for any offspring. Of course there are instances when two offspring arise from a single combination of two gametes giving rise to 'identical' twins who will be of the same gender and genetic makeup but not necessarily exactly the same depending on the physical influences on their existence.
Why will meiosis ensure that offspring have the same chromosome number as parents?
Ok...this is somewhat hard to explain without pictures.... Humans have 46 chromosomes in most cells. Meiosis makes a cell double its chromosomes to 96 and then the cell divides into two cells. Each (of those two cells) now has 46 chromosomes. Then, both cells divide again, leaving 4 cells with 23 chromosomes each. These four cells (not exactly right..but close enough for this) are either sperm or egg depending on if you are male or female.... So when a sperm (with 23 chromosomes) and egg (with 23 chromosomes) unite, the new cell (or baby) starts with 46 chromosomes. So, what meiosis does is ensures sex cells have HALF the number of chromosomes of an organism, so when two sex cells unite, the offspring has ONE full set of chromosomes.
Why aren't all human siblings identical?
There are two reasons why siblings are not identical. The first is genetic. Each child gets half of his or her DNA from the mother, and half from the father. But the total set of DNA is packaged into 23 different chromosomes. Each person has 46 chromosomes total, two of each. And in each of us, the two chromosomes are not the same.When your mother’s body creates an egg, 23 of the 46 chromosomes go into the egg, and it’s always one of each. But which one is random. So each egg is different. The same goes for the sperm made by your father’s body.This is most obvious in the fact that some children are boys, and others are girls. There is a special chromosome for determining gender. Women have two X chromosomes. Men have one X and one Y. Since a mother has two X chromosomes, every egg has one X chromosome. Meanwhile, on the dad’s side, he has an X and a Y, and so half his sperm have X and half his sperm have Y. When a sperm enters the egg at fertilization, if it is an X, the fertilized egg has two X, and a girl will grow. If the sperm has a Y, the fertilized has an X and a Y, and a boy will grow.All our other features work in a similar way, except in smaller genes, rather than in larger chromosomes.So, say that there is red hair on your mother’s side of the family, and she has red hair. And there’s red hair on your father’s side of the family, but he has black hair. Red hair is a recessive gene, so it only shows up as red hair if both genes are for red hair. One red and one black produces black hair, and so does two black hair genes.Your mother contributes one red hair gene to every egg. Your father contributes either a red hair gene (which he has, but it doesn’t show up) or a black hair gene. As a result, some children have red hair from two red hair genes, like mom, and some have black hair from one red and one black gene, like dad.It’s a lot more complicated than that, and all of this is about healthy cases, not genetic disorders. But this is enough to make the idea clear.The second reason is environmental. Even before we are born, our mother’s experience effects how we grow. Her nutrition, exercise, stress, even the music she listens to, all of these change our body and our growing mind long before we are born.That’s why we’re all unique, even brothers and sisters!
Do siblings who share the same set of parents each have the same distribution of parental DNA? Can one sibling have more of one parent's DNA or would the parental DNA distribution be equal?
First question: No, they do not.Reason: Recombination. Before an egg precursor cell splits a full set of paired DNA (diploid) into two egg cells with one set of DNA (haploid), the complementary DNA are somewhat randomly cut up and chunks swapped between them.Since this happens separately for each cell before it splits, each egg has a different mix of DNA in the chromosomes.The same thing happens when sperm are created in the male.So your mother got one set of DNA from her mother, and the other from her father. But when the egg is split into a haploid cell, any given chromosome consists of a mix of DNA from the chromosomes she received from her mother and her father. So you cannot say that, say, a chromosome that you received from your mother, came from your grandmother. Instead, it will be a mix of DNA from both your grandmother and your grandfather, due to recombination.The only chromosome for which this is not true are the X andY from the father, in which case a couple's daughters share an X from the father, and the sons share the Y from the father. No other chromosomes are untouched by recombination.Second question: It depends. Number of chromosomes, or total amount of DNA?Because each egg cell has 23 chromosomes, and each sperm cell has 23 chromosomes, each sibling will have an equal number of chromosomes from each parent. However, the Y chromosome is substantially smaller than the X chromosome, so technically girls have more DNA from their father than boys do.There are the somewhat rare cases of a boy inheriting two Y chromosomes from the father. Other mutations/mistakes involving multiple chromosomes don't seem to survive to birth.Thank you, Dan Theman, for correcting something I’d said about XYY. Despite what I’d been told long ago and the “popular wisdom”, there does not seem to be any particular correlation between XYY syndrome and any particular difficulties in behavior, intelligence, learning, or aggressive behavior.XYY syndrome - Wikipedia