Inheritance, Pedigrees, Karyotypes, Punnett Squares

Find this information in your text:genes on chromosomes page 350pedigrees pp 342-343karyotypes p 341 dominant & recessive alleles & what causes the

loss of function in proteins coded by recessive alleles pp264-265 and pp 345-347Punnett Squares p 268

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.

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).

223 or about 8 million possible ways exist to sort your two sets of 23 chromosomes into gametes!

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.

LE 14-4 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.

Allele for purple flowers

Homologouspair ofchromosomes

Allele for white flowers

Locus for flower-color gene

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)

Metaphase karyotype --colchicine used to trap cells at max condensation during metaphase of mitosis .Human body cells are diploid with 2n = 46. Why? Body cells are produced by asexual mitotic division. Human gametes are haploid with 1n = 23. Why? Gametes are produced by sexual meiotic cell division.

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 recessiveantennepia—legs instead of antennas—autosomal dominant!Colorblindness, boy in a bubble suit disease, hemophilia—sex linked recessive—

on the X csome in humansHuntington’s disease—too much huntington protein—autosomal dominant, late

onset, one of a few dominant and common inherited diseaseInherited breast cancer—BRCA genes inactive—no tumor suppressors—

autosomal dominantCertain inherited leukemias—translocation makes cell cycle control genes too

active and too abundant—dominant autosomal.

Ww ww ww Ww

Ww wwWwwwwwWw

WW ww

orWw

No widow’s peak

Thirdgeneration

(two sisters)

Recessive Trait: No Widow’s peak

Second generation(parents plus aunts

and uncles)

First generation(grandparents)

Dominant trait (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.

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.

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.

LE 14-14b

First generation(grandparents) Ff Ff

FF or Ff ff ff Ff Ff

ff

ff

Ff

Second generation(parents plus aunts

and uncles)

Thirdgeneration

(two sisters)

Attached earlobe Free earlobe

ff FForFf

Recessive trait (attached earlobe)

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

Pedigree for a disease caused by a dominant allele. No carriers! One disease

causing allele makes you sick.

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.

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 peakAttached earlobe—recessive—color person with attached earlobes

EE or Ee-free earlobe ee-attached earlobeHitchhiker’s thumb—recessive—color person who can bend thumb all

the way; half color (a carrier) a person who can bend it a littleHH-stiff thumb (no bend) Hh -bends a littlehh-up to a 90 degree backward’s thumb!

Tongue rolling—dominant—color person who can roll tongueTT or Tt-can roll tongue tt -can’t roll tongue

Curly hair—dominant cleft chin--dominantFreckles--dominant No hair on finger middle bond—recessiveRight over left thumb/hand-recessive bent pinky-dominant

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.

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.

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If you don’t finish in class, finish for homework.

Sample pedigree to do as a class.Bent finger (dominant trait)

Mom’s side of the family dad’s sideGreat GrandfatheryesGreat Grandmother noGrandfather no yesGrandmother yes noMother noFather yesChild no