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Genetics

Genetics. Chapter 11. Heredity. Passing of traits from parent to offspring. Genetics. The study of heredity Gregor Mendel- Austrian monk known as the “father of genetics”. Mendel’s Four Hypotheses. For each inherited trait, an individual has a copy of that gene from each parent.

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Genetics

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  1. Genetics Chapter 11

  2. Heredity • Passing of traits from parent to offspring

  3. Genetics • The study of heredity • Gregor Mendel- Austrian monk known as the “father of genetics”

  4. Mendel’s Four Hypotheses • For each inherited trait, an individual has a copy of that gene from each parent. • There are alternate versions of genes, called alleles. (ex: freckles or no freckles)

  5. Hypothesis continued • When 2 different alleles occur together, one of them may be completely expressed (dominant), while the other may not be observed (recessive). 4. Alleles separate independently, so that each gamete only carries 1 allele for that trait.

  6. Monohybrid cross • Mendel began with 1 trait (monohybrid) crosses • He bred pea plants to produce several generations P- the parent generation F1 - the first filial generation F2 - second filial generation

  7. Mendel concluded that each parent has two separate “factors” for a particular trait • “Factors” are now called genes.

  8. Mendel’s Laws of Heredity • Law of Segregation- two alleles separate when gametes are formed • Law of Independent Assortment- alleles of different genes separate independently of one another during gamete formation

  9. Homozygous dominant parent Homozygous recessive parent Mendel’s Law of Segregation (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring Fig. 11-5, p.172

  10. Independent Assortment Nucleus of a diploid (2n) reproductive cell with two pairs of homologous chromosomes Possible alignments of the two homologous chromosomes during metaphase I of meiosis The resulting alignments at metaphase II Allelic combinations possible in gametes 1/4 AB 1/4 ab 1/4 Ab 1/4 aB Fig. 11-8, p.174

  11. Some modern genetic terms • Alleles are represented by letters • Dominant allele is a capital letter • Recessive allele is a lower case letter

  12. Homozygous- identical alleles for a specific trait (BB, FF, rr, tt) • Heterozygous- alleles are different for a specific trait (Bb, Ff, Rr, Tt) (aka “hybrid”) • Genotype- the set of alleles an individual inherits for a trait (i.e.- Rr, Ww, ff) • Phenotype- the physical expression of a trait (i.e. blue eyes, freckles, dimples)

  13. Punnett Square • Predicts possible outcomes of traits • Shows all possible outcomes of a genetic cross

  14. Probability (likelihood that an event will occur) of a genetic outcome can be predicted • Ex: cross two heterozygous individuals Aa x Aa predict ratios of 3:1 for phenotype and 1:2:1 for genotype

  15. Practice • Curly hair is dominant over straight hair. A man with straight hair and a woman who is heterozygous for curly hair have a child. What is the probability that this child will have straight hair?

  16. Incomplete Dominance- when an individual shows a combination of the inherited alleles. Ex: red snapdragon x white snapdragon will produce a pink snapdragon straight hair x curly hair = wavy hair

  17. Codominance- 2 dominant alleles are expressed at the same time Ex: Roan horses show both red and white hairs in equal numbers

  18. Patterns of heredity can be very complex • Sex-linked trait- a trait whose alleles is located on the X chromosome (most are recessive) • Polygenic trait- trait where several genes influence the outcome (eye color, hair color, skin color, height, weight)

  19. Multiple Alleles- genes with 3 or more alleles - Blood type is an example of multiple alleles because we have A, B and O alleles and 4 possible blood type outcomes (A, B, AB and O)

  20. ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii Blood Types: A AB B O Fig. 11-10a, p.176

  21. Diploid • Number of chromosomes found in the body or somatic cells of an organism • “2n”

  22. Haploid • Number of chromosomes found in the gametes of an organism • “n”

  23. Meiosis • The type of cell division that produces gametes • Gametes = sex cells • female gamete = egg or ovum (plural = ova) • male gamete = sperm

  24. Meiosis

  25. Formation of sperm and egg

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