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Genetics

Explore the fascinating realm of genetics with an overview of heredity, Mendel's laws, Punnett squares, and modern genetic terms. Discover how traits pass from parent to offspring and delve into alleles, genotype, and phenotype.

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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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