Genetics

Study of Heredity Why do cats have kittens and not puppies? Why do humans give birth to other humans? What controls what your child will look like? Genetics: the study of heredity Heredity: passing of traits from parents to offspring.

Imagine a time before we knew of DNA and genes. These things were a great mystery.

Original Ideas in Genetics Blended Inheritance: –Mother’s traits and Father’s traits are blended to make the child’s traits. A strong man and a weak woman would have a child with average strength. We know this is not true today, because of Gregor Mendel.

Gregor Mendel Born in Austria in 1822 Became a monk Worked in the monastery garden Was interested in science Began to experiment with peas.

Mendel cross-fertilized peas Why peas? –Reproduce really quickly –Could control the matings of pea plants –Peas are Hermaphrodites –Grows easily and produces MANY offspring

What did he do? Self-pollinated two different plants This made each plant true-breeding. Finally, he had two separate true-breeding plants that he could cross-pollinate.

Vocabulary Self-pollination-letting the male part of one plant fertilize the female part of the same plant. (Hermaphroditic part) AKA:inbreeding True-breeding-a plant that produces offspring that display only one form of a trait. (Ex- purple plant makes purple plants) Cross-pollination-letting the male part of one plant fertilize the female part of a different plant (more like dating)

What traits did Mendel look at? Seed shape Seed color Pea Pod shape Pea Pod color Flower color Flower position Plant size

Mendel had specific names for each generation of plants. P generation –Parental generation, the first two individuals that are crossed in a breeding experiment. F 1 generation –First filial generation, the offspring of the P generation F 2 generation –Second filial generation, the offspring F 1 generation

As Mendel worked, he discovered… Blending inheritance was not correct! Wrinkled + smooth peas = –No half-wrinkled peas!!! –Only fully wrinkled or smooth peas. –With continued work, he discovered…..

….that “lost” traits reappear.

Mendel’s Four Hypotheses Mendelian Theory of Heredity –1. When gametes are formed, only one allele for each gene goes into each gamete. This happens during Meiosis II. There’s only one allele in each sperm and only one allele in each egg. –2. An individual gets two genes for each trait (one from each parent) Each pea plant gets one gene for pod color (one from each parent plant) –3. These two genes are called Alleles and there are different versions of alleles For the pea pod color trait: yellow or green or white, etc. –4. Of these different versions of alleles, one is dominant and one is recessive For the pea pod trait : Green alleles are dominant, yellow alleles are recessive

What does this mean? Example: You have two genes (alleles) for each trait. 1. Your Gametes have half of your chromosomes (only 1 of the pair of allele for each trait). 2. At fertilization, the embryo gets one allele from each parent. In this case, you get Mom’s allele for wrinkles and Dad’s allele for smoothness (3. There are different versions of alleles). 4. Of the different versions of alleles, one is dominant and one is recessive. Dominant = smoothness Recessive = wrinkled

What do you mean by dominant and recessive? Example: 1 allele for wrinkles (recessive) 1 allele for smoothness (dominant) You have 1 dominant and 1 recessive allele. The dominant shows through, masking the recessive allele. You appear smooth! The dominant allele always shows through, masking the recessive allele. The recessive allele only shows through when there is no dominant allele present.

We represent alleles with letters. Example: Trait: Pea pod color Alleles: 1 wrinkled, 1 smooth Smooth = dominant Wrinkled = Recessive **Dominant alleles are written with capital letters and Recessive alleles are written with lower-case letters. Ss Will this pea appear smooth or wrinkled and how do you know? Smooth, because the dominant allele will mask the recessive allele. Another One: Trait: Eye color Alleles: 1 blue, 1 brown Brown = dominant Blue = Recessive Bb What color eyes will this person have? Brown

A couple more…. Trait: Eye color Alleles: 2 blue Brown = dominant Blue = Recessive bb What color eyes will this person have? Blue! Trait: Freckles Alleles: 1 freckles, 1 no freckles No freckles = dominant Freckles = Recessive Ff Does this person have freckles? Yes

Some vocabulary Try identifying the following combinations of alleles: Tt heterozygous jjHomo. Recess. Llheterozygous MM Homo. Dominant Homozygous Dominant –Both alleles are dominant, BB (both are capital letters) Homozygous Recessive –Both alleles are recessive, bb (both are small letters) Heterozygous –One allele is recessive, the other is dominant –Bb (one capital, one brown small) –**Always write the dominant/capital letter first.

A few last terms! Genotype –Set of alleles that an individual has (letters) –Bb Phenotype –Physical appearance of the individual (what you see) –Brown eyes

Determine the genotype of the following individuals. An alien has 1 allele for wings and 1 allele for no wings. (Wings are dominant) Ww An alien has 2 alleles for striped fur. (Striped fur is recessive) nn An alien has three eyes. (Three eyes is a recessive trait) ff

Determine the phenotype of the following individuals. An alien has 1 allele for wings and 1 allele for no wings. (Wings are dominant) It has wings. An alien has 2 alleles for striped fur. (Striped fur is recessive) It has striped fur. An alien has a genotype tt. (t = allele for three eyes, which is a recessive trait) It has three eyes. An alien with the genotype Rr. (R=red eyes, r=purple eyes) It has red eyes.

Understanding how traits are inherited is important! Traits like eye color and hair color, but also heritable diseases like Cancer. So scientists want to know the probability of passing on these diseases. To calculate probabilities, geneticists use Punnett squares.

Let’s say that you and your husband go to a geneticist and discover that you both are heterozygous for Huntington’s Disease! What are the chances of your children inheriting the disease? Mom’s gametes Dad’s gametes Dad’s genotype: Rr Mom’s genotype: Rr

Let’s analyze this Punnett Square!

1 out of 4 will be homozygous dominant (RR) 2 out of 4 will be heterozygous (Rr) 1 out of 4 will be homozygous recessive (rr) Which genotype will result in Huntington’s Disease? –The “rr” genotype only! So your chances of having a child with Huntington’s Disease is ¼ or 25%.

Try one on your own! Cross a mother with the genotype Dd and a father with the genotype DD. What are the chances that their child will have the genotype DD, like Daddy?