Introduction To Genetics- Chapter 11 1

The work of Gregor Mendel Gregor Mendel was born in 1822 and after becoming a priest; Mendel was a math teacher for 14 years and a monastery. Mendel was also in charge of the monastery garden.. 2

Mendel carried out his work with garden peas 3

Fertilization is the fusion of an egg and a sperm. True breeding plants are plants that were allowed to self-pollinate and the offspring would be exactly like the parent. 4

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Genes and Dominance The different forms of a gene is called and an alleles. 1. The principle of dominance states that some alleles are dominant and others are recessive. 6

7 Pinky Finger Traits At John Burke High School they tested dominant and recessive traits in our school population. We tested pinky finger traits, whereby, the bent finger is dominant and the straight finger is recessive.

Segregation Each trait has two genes, one from the mother and one from the father. Traits can be either dominant or recessive. A dominant trait only needs one gene in order to be expressed. 8

A recessive trait needs two genes in order to be expressed. 9

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Egg and sperm are sex cells called gametes. 2.The Principle of Segregation – Segregation is the separation of alleles during gamete formation. 11

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Probability and Punnett Squares Genetics and Probability – The likelihood that a particular event will occur is called probability. – The principals of probability can be used to predict the outcome of genetic crosses. 13

PROBABILITY 14

Lets Predict: Punnett Squares The gene combination that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. Punnett squares can be used to predict and compare the genetic variations that will result from a cross. 15

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Each trait has two genes- one from the mother and one from the father. Alleles can be homozygous – having the same traits. Alleles can be heterozygous- having different traits. 17

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Physical characteristics are called the phenotype. Genetic make up is the genotype. 19

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Exploring Mendalian Genetics 3. The Principle of Independent assortment – Genes segregate independently. 21

The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals and other organisms. 22

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A summary of Mendel ’ s Principals Genes are passed from parent to offspring. Some forms of a gene may be dominant and others recessive. 24

In most sexually producing organisms, each adult has two copies of each gene- one from each parent. These genes are segregated from each other when gametes are formed. The alleles for different genes usually segregate independently of one another. 25

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Review (PDN) What does it mean to be “dominant” and “recessive”?? How can you write out “dominant” and “recessive”? -- use brown hair (B) is dominant over red hair (b) 27

Beyond Dominance and Recessive Alleles Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Cases in which one allele is not completely dominant over another are called incomplete dominance. 28

Example: White (W) and Red (R) is both dominate. If WW X RR the F1 generation would be What? 29

Red=R White=W 1. Cross a red flower with a white flower, showing incomplete dominance. RR W W R R R R W W W W Genotype: 100% RW Phenotype: PINK!

Incomplete dominance: Alleles are expressed as a blend. Each allele has a capital letter. Red= R Yellow= Y

Codominance is when both alleles contribute to the phenotype. Example: Feather colors 34

Codominance seen separately Both traits dominate, seen separately! Red Horse White Horse

Give you ROAN!

Example of Codominant Problem Red feathers are codominant to white feathers in chickens. C R = red C W = white Cross a homozygous Red with a homozygous white feathered chicken. CRCR CRCR CWCW CWCW CRCR CWCW CRCR CWCW CRCR CWCW CRCR CWCW PHENOTYPE: 100% Red and white mixed feathers CRCR CWCW GENOTYPE: 100%

Many genes have more than two alleles and are referred to have multiple alleles. This means that more than two possible alleles exist in a population. – Like eye color… hair / fur color… 38

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One trait, many allele options! But remember: an individual cannot inherit more than two actual alleles, even if more than two possible alleles exist. Another Example: Blood type A, B, AB, O!

Rabbits have 4 basic colors (alleles!) brown chinchilla or grey It is recessive to brown. himalayan or white with black tips. It is recessive to both brown and chinchilla. albino It is recessive to all.

AIbino Himalayan Chinchilla Full color

Polygenic Traits Traits produced by many genes with many alleles Most human traits are polygenic Most variety of expression There are 3 genes that contribute to skin color.. And many alleles for each gene!

Traits that are controlled by two or more genes are said to be polygenic traits, which means, “ having many genes. ” Example: eye color has many different genes. 44

More examples: Height Weight Intelligence Eye color

Sex Determination In humans, the X and Y chromosomes control the sex of offspring. Outcome is always 50% chance of a male, and 50% chance of a female

Sex-linked traits Traits controlled by genes on the sex chromosomes are called sex-linked. Alleles for sex-linked traits are written as superscripts on the X chromosomes only. Traits controlled by genes on the sex chromosomes are called sex-linked. Alleles for sex-linked traits are written as superscripts on the X chromosomes only. XRXR XRXR XrXr y Example: Red eyes in fruit flies found in females Males tend to have white eyes, which is recessive.

X and Y sex chromosomes are non- homologous Any allele on the X chromosome will NOT be masked by a matching allele on the Y chromosome.

Why are sex-linked disorders more common in males than in females? Males have just one X chromosome containing an allele. So all X-linked alleles are automatically expressed in males, even if they are recessive.

Why is Mendel’s Work so IMPORTANT?? Applying Mendel ’ s principles Mendel ’ s principals do not only apply to plants. 51

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