The first illustration shows a Father and Mother with brown eyes. Both parents have only dominant genes for brown eyes which is depicted by the combination BB in the illustration. Consequently, only B is possible from the sperm of the Father as well as the egg of the Mother. All offspring from these parents will therefore have only brown eyes.
The caption below the illustration reads, Both parents have only dominant genes for brown eyes, so that is the only genetic information they can pass to their children. All their children will have brown eyes.
In the second illustration, the father has a recessive gene for blue eyes, represented genetically as bb and the mother, dominant genes for brown eyes represented genetically as BB. In this case, only a blue b is possible from the father and a brown B from the mother. As the father only has recessive genes for blue eyes, the mother’s dominant genes are passed on to any offspring.
The caption below the illustration reads, The father only has recessive genes for blue eyes, so that is all he can pass along to his child. The mother only has dominant genes for brown eyes, so that is all she can pass along. Each child will have one gene for blue eyes and one gene for brown eyes, so all the children will have brown eyes.
In the third illustration, both parents are shown to possess a recessive gene for blue eyes represented genetically as bb. All offspring will therefore have only blue eyes and possess the recessive gene for blue eyes represented by bb.
The caption below the illustration reads, Both parents only have recessive genes for blue eyes. They both have blue eyes and can only pass genes for blue eyes to their children, so all their children will have blue eyes.
The fourth illustration shows both parents possess a dominant gene for brown eyes and a recessive gene for blue eyes represented genetically as Bb. In this case, an offspring can have either brown or blue eyes depending on the gene they receive from each parent. If the offspring has the bb combination, it will have blue eyes. However, if it has the Bb or BB combination, the child will have brown eyes.
The caption below the illustration reads, Each parent has both a dominant gene for brown eyes and a recessive gene for blue eyes (so both have brown eyes). However, if each passes along a recessive gene for blue eyes, the child will have blue eyes, but if either parent passes along a gene for brown eyes, the child will have brown eyes.
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This figure shows a cross section of a blood vessel with normal red blood cells as well as another with abnormal sickled red blood cells. A cross section of a normal and sickle red blood cell are also seen.
The image A on the left, shows red blood cells flowing through a blood vessel as well as a cross section of a red blood cell (RBC). The normal cell contains normal hemoglobin.
Image B on the right, shows abnormal sickled red blood cells also known as sickle cells. A cross section of the blood vessel shows sickle cells blocking the blood flow through the vessel due to their abnormal shape. A cross section of this cell is also shown where abnormal hemoglobin forms strands that cause sickle shape.
The caption below the image reads, Normal red blood cells move freely through the blood vessels (a). sickle-shaped red blood cells stick together and block the normal flow of blood, depriving the organs of needed oxygen (B).
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The first image shows a long needle used to extract amniotic fluid from the amniotic sac by using an ultrasound as a guide.
The image on the right shows a catheter being used to extract amniotic fluid.
The caption below the images read, During amniocentesis (shown on the left), a physician uses an ultrasound to show a picture of the fetus in the amniotic sac and then uses a long, thin needle to extract about 4 teaspoons of amniotic fluid. Fetal cells floating in the fluid can be tested for genetic problems. In chorionic villus sampling (shown on the right), an ultrasound is also used to guide a mall tube, or catheter, which is inserted either through the vagina and cervix or through a needle inserted in the abdomen, and a sample of cells from the chorion (which has the same genetic makeup as the fetus) is retrieved for testing.
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The genetic similarities between siblings, identical and fraternal twins is illustrated here.
The first image shows two eggs, one fertilized by a sperm and the other unfertilized. Here, a single egg is fertilized by a single sperm. Each parent contributed one half of the individual’s genetic makeup.
The second image shows two rows of eggs with a sperm fertilizing an egg on each row, the other unfertilized. In two separate pregnancies, a single egg is fertilized by a single sperm. This illustration represents siblings. Each sibling shares 50% of his or her genetic makeup with the other sibling.
The third image shows two rows of eggs with a sperm fertilizing an egg on each row, the other unfertilized. Two eggs are released during a single menstrual cycle and each is fertilized by a different sperm. This illustration represents fraternal twins. Fraternal twins are as genetically similar as any two siblings. They share 50% of their genetic makeup.
The fourth image shows two eggs. Here, a single egg is fertilized by a single sperm. The resulting zygote splits early in development into two identical conceptions. This illustration represents identical twins. Identical twins come from a single fertilized egg, so they have almost all of their genes in common.
The caption below the images reads, The difference in the degree of gene similarity of identical and fraternal twins as shown in this figure has been used by researchers to study the effect of genes on many human characteristics.
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This figure shows a series of carved gullies at the bottom of a hill with various balls rolling down the hill. Each ball has stopped at a different stage based on where it started.
Some balls start on the shallow side have also stopped on the shallower gullies and those that have started on the steep side have stopped at the steeper, narrower gullies.
The caption below the image reads, When a trait is deeply canalized, it is similar to a ball rolling down a deep gully. Just as a deeply canalized trait results in similar outcomes regardless of circumstances, the balls will always arrive in about the same place (balls in the deeper gullies). When a trait is less deeply canalized, the outcomes can vary depending on circumstances. In this case, where the balls rolling down a shallow gully end up will depend on circumstances and show greater variability (balls in the shallow gullies).
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This illustration shows epigenetics where the experiences of an individual activates or subdues the chemical tags in the DNA of genes.
This illustration shows a histone that is a spool around which DNA winds. This histone is represented by a circle with four segments around which a DNA strand is wrapped. Histone tails are also visible in two segments of the histone. Also visible are two other histones in the illustration, all of which are connected by DNA wrapped around them. A DNA segment connecting the first and second histone highlights a segment marked DNA Accessible, Gene turned on. Chemical tags, attached to the histone tails, are visible on both the histones.
The illustration also shows a group of five histones wound together by DNA where now, the highlighted part of the DNA is inaccessible and the gene is turned off. These histones are then shown as a part of a chromosome with the DNA now inaccessible as the gene is turned off.
The caption below the image reads, Chemical tags in the DNA of genes can be activated or silenced by an individual’s experiences. The tags allow certain genes to be read or cause them to be hidden. The basic structure of the DNA does not change, but the expression of the gene does. In this figure, chemical tags determine whether DNA winds tightly around histones or unwinds, permitting the expression of the genes.
4 Prenatal Development, the Newborn, and the Transition to Parenthood