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Inheritance, Pedigrees, Karyotypes, Punnett Squares

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Presentation on theme: "Inheritance, Pedigrees, Karyotypes, Punnett Squares"— Presentation transcript:

1 Inheritance, Pedigrees, Karyotypes, Punnett Squares
Find this information in your text: genes on chromosomes page 350 pedigrees pp karyotypes p 341 dominant & recessive alleles & what causes the loss of function in proteins coded by recessive alleles pp and pp Punnett Squares p 268

2 Humans reproduce sexually
Humans reproduce sexually. This means females produce eggs (ova) carrying only one of each chromosome—total 23, while males produce sperm carrying only one of each—total 23. When sperm and egg unite at fertilization, a zygote with a full double set of chromosomes—total 46—is formed.

3 It’s random which set of your 23 homologous chromosomes you’ll sort (by cell division called meiosis) to each gamete. This drawing (organism w/ 2 kinds of chromosomes) shows 2n combinations of chromosomes possible (n=# different types chromosomes)in gametes (sperm or eggs) or about 8 million possible ways exist to sort your two sets of 23 chromosomes into gametes!

4 Meiosis is a type of cell division that results in your giving one of each chromosome to your child in a sex cell, sperm or egg. Having one copy of each chromosome is called haploid.

5 Because offspring have 2 of each type of chromosome, they have 2 copies of each gene. Offspring may receive identical versions of the gene (alleles) from both parents and be homozygotes OR they may receive different alleles from the two parents and become heterozygotes. LE 14-4 Allele for purple flowers Locus for flower-color gene Homologous pair of chromosomes Allele for white flowers

6 A map of the human X chromosome showing that it always carries the same genes in the same order. The smaller Y is lacking most of these genes, so boys more commonly inherit recessive diseases associated with these diseases (called sex linked diseases)

7 Metaphase karyotype --colchicine used to trap cells at max condensation during metaphase of mitosis . Human body cells are diploid with 2n = Why? Body cells are produced by asexual mitotic division. Human gametes are haploid with 1n = Why? Gametes are produced by sexual meiotic cell division.

8 Genes carry out the jobs of a cell
Genes carry out the jobs of a cell. If critical jobs are done by a protein, then mutations that alter its function can cause genetic disorders. Diabetes—no insulin made (recessive) Tay Sachs –no brain lipid digesting enzyme made (recessive) Dwarfism—no growth factor made (recessive) Albinism—no pigment for skin, hair, eyes made (recessive) Cystic fibrosis—no salt channel made to allow ions of salt to escape cells recessive antennepia—legs instead of antennas—autosomal dominant! Colorblindness, boy in a bubble suit disease, hemophilia—sex linked recessive—on the X csome in humans Huntington’s disease—too much huntington protein—autosomal dominant, late onset, one of a few dominant and common inherited disease Inherited breast cancer—BRCA genes inactive—no tumor suppressors—autosomal dominant Certain inherited leukemias—translocation makes cell cycle control genes too active and too abundant—dominant autosomal.

9 Recessive Trait: No Widow’s peak
Pedigrees are family trees showing whether each person does (filled in) or does not (not filled in) have a particular trait. Males are shown as □ & females as O. Ww ww ww Ww First generation (grandparents) Ww ww ww Ww Ww ww Second generation (parents plus aunts and uncles) Third generation (two sisters) ww WW or Ww No widow’s peak Dominant trait (widow’s peak) Recessive Trait: No Widow’s peak

10 Cleopatra (Queen of Egypt, descended of the Pharoahs)
Cleopatra (Queen of Egypt, descended of the Pharoahs). Since Pharoahs were considered god-like, they were only able to marry people of the same status.

11 Cleft palate, club foot, severe scoliosis, other bone disease
2/17/2010, King Tut’s 5 generation pedigree was published (DNA tests of blood cells in mummies) Tut’s parents were brother and sister, and Tut was married to his sister. King Tut had several obvious disorders, likely due to double doses of recessive alleles from his brother/sister parents: Cleft palate, club foot, severe scoliosis, other bone disease Tut’s own two children were still-born.

12 Recessive trait (attached earlobe)
LE 14-14b First generation (grandparents) Ff Ff ff Ff Second generation (parents plus aunts and uncles) FF or Ff ff ff Ff Ff ff Third generation (two sisters) ff FF or Ff Attached earlobe Free earlobe Recessive trait (attached earlobe)

13 Pedigree for a disease caused by a recessive allele
Pedigree for a disease caused by a recessive allele. Note that marrying a relative increases changes of inheriting 2 recessive alleles.

14 Pedigree for a disease caused by a dominant allele. No carriers
Pedigree for a disease caused by a dominant allele. No carriers! One disease causing allele makes you sick.

15 Geneticists use pedigrees to locate relatives who are healthy versus ill due to inherited disease. Comparing their data allows the defective gene to be identified.

16 Construct pedigrees for your own family’s trait data
Construct pedigrees for your own family’s trait data. Use the pedigree to determine as many genotypes (the 2 forms of the alleles) as possible. Widow’s peak—dominant—color symbol if person has widow’s peak ww -no widow’s peak Ww or WW -has widow’s peak Attached earlobe—recessive—color person with attached earlobes EE or Ee-free earlobe ee-attached earlobe Hitchhiker’s thumb—recessive—color person who can bend thumb all the way; half color (a carrier) a person who can bend it a little HH-stiff thumb (no bend) Hh -bends a little hh-up to a 90 degree backward’s thumb! Tongue rolling—dominant—color person who can roll tongue TT or Tt-can roll tongue tt -can’t roll tongue Curly hair—dominant cleft chin--dominant Freckles--dominant No hair on finger middle bond—recessive Right over left thumb/hand-recessive bent pinky-dominant

17 Punnett Squares allow you to predict all the possible combinations of gene alleles that mates might pass to children. Here is an example for a father having one A and one a allele and a mother having one A and one a allele. By random chance of which gametes are passed, about ¼ of their children should have two recessive alleles.

18 For your traits of tongue rolling, hitchhiker’s thumb, widow’s peak, and ear attachment, create a Punnett square for possible allele combinations that you and one other person in the class might pass to children if you mated. Use the Punnett square results to estimate the fraction of your children who would have each of the traits If you don’t finish in class, finish for homework.

19 Sample pedigree to do as a class. Bent finger (dominant trait)
Mom’s side of the family dad’s side Great Grandfather yes Great Grandmother no Grandfather no yes Grandmother yes no Mother no Father yes Child no


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