Heredity: Passing down Genes

Gregor Mendel: Father of Genetics Gregor Mendel was born in 1822 in Austria. He grew up on his family’s farm and was able to learn a lot about flowers and fruit trees. After going to college, he joined a monastery. At the monastery, he worked in the garden where he studied how traits were passed form parent to offspring.

Mendel noticed that some patterns of inheritance made sense and other did not. For example, Mendel noticed that when he crossed a purple flowered pea plant with a white flowered pea plant, that all of the offspring had purple flowers. He then noticed that if he crossed two of these offspring, then one out of every four offspring had white flowers. Mendel wanted to know why.

Pea Plant Fertilization The flowers of pea plants are self-pollinating which means that they contain both male and female reproductive structures. 􀂋 Pollen from one flower or plant can fertilize the eggs of the same plant or another plant.

Pea Plant Fertilization Mendel cut off the anthers of one flower and used the pollen from these anthers to fertilize the stamen on another plant. For example, he used the pollen from a plant that produced wrinkled seeds to fertilize the plant that produced round seeds. The stigma of the flower actually turns into seeds (peas). These seeds/peas are then planted in the ground to produce more pea plants.

Pea Plant Fertilization Mendel looked at 7 traits of pea plants. Mendel crossed pea plants with two different forms of each trait (for example, smooth/wrinkled peas or yellow/green peas) to determine which traits would appear and how often. Mendel was then able to determine which of the 7 traits were dominant and which were recessive.

Dominant & Recessive Dominant = genes that “take over” – they are “stronger” and the dominant trait will show over the recessive trait. Dominant genes are shown in UPPER CASE LETTERS. Recessive = genes that are “weaker” and will not show if a dominant gene is present. Recessive genes are shown in lower case letters. Each parent has two genes (or letters) for a trait. These letters are called alleles.

Dominant & Recessive Traits in Pea Plants

Dominant & Recessive Traits in Pea Plants

Which gene do you have? Dominant B – brown eyes T – tall C – curly hair W – widows peak F – freckles A – free ear lobes D – Dimples C – Cleft chin Recessive b – blue eyes t – short s – straight hair w – no widows peak f – no freckles a – attached ear lobes d – no dimples c – no cleft chin

Write down your traits below:

Genotype and Phenotype Phenotype: The inherited genes physical look. Genotype: Inherited alleles (letters of genes) Genotype: Bb Genotype: BB Genotype: bb Phenotype: Brown eyes Phenotype: Blue eyes

Homozygous and Heterozygous Genes that are the same Heterozygous = Genes that are different

Gender determination Female – XX Male –XY Male determines the sex of the baby

Sex-linked traits Some traits such as baldness & colorblindness are sex-linked traits They are found on the male and female chromosomes X X = normal vision X Y = color blindness

Punnett Squares Using Punnett Squares allow us to show what the offspring could look like. Allows us to calculate probability of certain genotypes and phenotypes to occur

Complete a Punnett Square for the Homozygous First Generation Rabbits below:

Complete a Punnett Square for the second generation heterozygous bunnies:

Punnett Square Questions: What is the probability that the homozygous rabbit’s offspring will be black? What is the probability that the offspring will be white? For the second generation, what is the probability the offspring will be black? What is the probability the offspring will be white for 2nd generation?

Incomplete Dominance Example: A red flower allele and a white flower allele creates a pink flower. If it were co-dominant you would see the red and white colors. Incomplete dominance is most commonly found in plants. A form of inheritance in which the heterozygous alleles are both expressed, resulting in a combined (or mixed) phenotype.

Co-Dominance A form of inheritance in which both alleles are equally shown. Blood typing is a great example. AB blood is the co-dominant relationship between the A protein and B protein both expressing themselves completely.

Polygenic Traits =Polygenic traits are the result of the interaction of several genes. For instance, phenotypes like high blood pressure (hypertension) are not the result of a single "blood pressure" gene with many alleles . The phenotype is an interaction between a person's weight (one or more obesity genes), cholesterol level (one or more genes controlling metabolism), kidney function (salt transporter genes), & smoking (a tendency to addiction).

Multiple Alleles A single gene having many alleles (A, a, A1, A2, A'). For example, hair color in mice is determined by a single gene with a series of alleles, each resulting in different coloration. There are alleles for black, brown, agouti, gray, albino, and others. The twist here is that the same allele can be dominant or recessive depending on context. Allelic series are often written as agouti > black > albino.