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Chapter 8 Mendel

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Chapter 8 Mendel & Heredity I. Terms Heredity- the passing on of traits (color/shape of eyes, texture of hair) from parent to offspring Genetics- the study of ... – PowerPoint PPT presentation

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Title: Chapter 8 Mendel


1
Chapter 8 Mendel Heredity
2
I. Terms
  • Heredity- the passing on of traits (color/shape
    of eyes, texture of hair) from parent to
    offspring
  • Genetics- the study of heredity
  • Genes- pieces of DNA that code for a certain
    trait (Mid-digital hair)
  • Alleles- alternative versions for each gene
  • (ex. hairy mid-digits, non hairy mid-digits)
  • 1) Letters are used to represent alleles
    (Capital letters represent dominant trait, lower
    case represent recessive trait)

3
Terms continued
  • Homozygous- 2 alleles in an individual are the
    same (ex. HH, hh), pure bred
  • Heterozygous- alleles are different (ex. Hh),
    hybrid
  • Genotype- the set of alleles that an individual
    has (ex. HH, Hh, hh)
  • Phenotype- the physical appearance of a trait
    (ex. Hairy mid-digits, non hairy mid digits)

4
II. Gregor Mendel
  1. Gregor Mendel (1800s) - Father of Genetics
    p.161
  2. http//science.discovery.com/videos/100-greatest-d
    iscoveries-shorts-genetics.html

5
Mendel
  • Studied 7 traits in garden peas (grows quickly
    produces many offspring)
  • Traits- pod color, flower color, wrinkled,
    height, seed shape, etc.
  • -Self-pollination produced the same traits every
    time
  • Ex. Purple x Purple All Purple flowers
    White x White All White

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  • Crossed 2 plants with contrasting traits
  • (P1 x P1 F1)
  • Ex. Pure white x Pure purple All purple plants
    F1 (filial) generation
  • 2nd cross between plants of F1 generation yielded
    the F2 generation
  • F1(purple) x F1 (purple) F2 (75 purple 25
    white)
  • (Before Mendel, people thought offspring were a
    blend of their parents
  • Ex. Tall x Short Medium height)

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C. Mendelian theory of heredity
  • 1. For each trait, an individual has two copies
    of the geneone from each parent
  • 2. There are alternative versions of genes
    (alleles)
  • 3. The allele that is displayed is called
    dominant the allele that is present in the
    organism but has no effect on its appearance is
    called recessive

10
1.Law of Segregation the two alleles for the
trait separate when gametes are formed. Gametes
carry only one allele for each inherited trait
11
2. Law of independent assortment the alleles of
different genes separate independently of one
another when gametes are formed.
12
III.Punnett square
  • A. Tool used by scientist to predict the
    outcome of a genetic cross

13
  • Monohybrid sample problem
  • In roses, red is dominant over white.
  • Use R for the red gene.
  • Use r for the white gene.
  • Cross two heterozygous red roses, Rr X Rr
  • From the Punnett Square,
  • describe the phenotype of the offspring.
  • 3/4 Red
  • 1/4 White
  • describe the genotype of the offspring.
  • 1/4 RR
  • 1/4 rr
  • 2/4 (or ½) Rr
  • lt/TD

14
IV. Beyond Complete Dominance
  1. Incomplete dominance- when neither allele is
    dominant over the other results in blending the
    heterozygous genotype (Rr)

15
Examples
  • Incomplete Dominance
  • 1. One trait in humans that is displayed by
    incomplete dominance is hair texture. The
    heterozygous genotype (Hh) is expressed as wavy.
    If mom has curly hair, which is dominant to
    straight hair, and dad has wavy hair then what is
    the probability of them having an offspring that
    has curly hair?

Can they have an offspring that has straight
hair?
16
B. Co-dominance- both alleles are expressed in
the heterozygote equally
Ex. Multiple alleles inheritance (blood type)
17
Example
  • Co-dominance
  • 2. Roan cattle are a result of co-dominance.
    List the possible phenotypes of the offspring
    that would result from the crossing of 2 roan
    cattle.

18
  • C. Sex-linked inheritance- traits carried on the
    X chromosome
  • ex. color blindness (red/green),
  • hemophilia (blood clotting disorder)
  • Punnett Square Examples
  • XXfemale
  • XYmale

19
More Examples of Sex-Linked Recessive Disorders
  • Red/Green Colorblindness Difficulty perceiving
    differences between colors (red or green, blue or
    yellow).
  • Hemophilia Absence of one or more proteins
    necessary for normal blood clotting.
  • Deafness
  • Cataracts opacity in the lens that can lead to
    blindness
  • Night blindness (Nyctalopia) rods do not work
    so that can not see in the dark
  • Glaucoma pressure in the eye that can lead to
    optic nerve damage and blindness
  • Duchenne Muscular Dystrophy progressive
    weakness and degeneration of skeletal muscles
    that control movement due to absence of
    dystrophin (protein that maintains muscle
    integrity). Mainly in boys, onset 3-5 yrs, by 12
    years cant walk, and later needs respirator.

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Example
  • Sex-linked disorders
  • 3. Hemophilia is a blood clotting disorder that
    is sex-linked recessive disorder (found on the X
    chromosome). Demonstrate a cross between a mom
    who is a carrier for the disorder and a dad who
    does not have hemophilia.

a) What percent of the offspring will have
hemophilia? b) What percent of the females are
carriers? c) What percent of the males have
hemophilia?
22
Example
  • Sex Linked Inheritance Co-dominance
  • 4. Coat color in cats is a co-dominant trait
    and is also located on the X chromosome. Cats
    can be black, yellow or calico. A calico cat has
    black and yellow splotches. In order to be
    calico, the cat must have an allele for the black
    color and an allele for the yellow color.

23
  • 4. A female calico cat is crossed with a male
    black cat.
  • a) What percent of the offspring are calico?
  • b) What percent of the females are calico?
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