Study of heredity

What is Genetics? Heredity: passing of traits from parent to child Patterns of relatedness can help predict offspring characteristics –Autosomal recessive –Autosomal dominance –Sex-Linked –Incomplete dominance –Codominance

Genes are located on chromosomes Genes inherited from mom and dad Genes come in several forms called alleles

–Allele: Alternative forms of a gene –Ex: Flower color White allele or Purple allele

An allele is any alternative form of a gene occurring at a specific locus on a chromosome. –Each parent donates one allele for every gene. –Homozygous describes two alleles that are the same at a specific locus. –Heterozygous describes two alleles that are different at a specific locus.

Alleles can be represented using letters. Ex: Aa or AA or aa –A dominant allele is expressed as a phenotype when at least one allele is dominant. –A recessive allele is expressed as a phenotype only when two copies are present. –Dominant alleles are represented by UPPERCASE letters –Recessive alleles by lowercase letters.

Dominant and Recessive Genes Gene that prevents the other gene from “showing” – dominant Gene that does NOT “show” even though it is present – recessive Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t Dominant color Recessive color

Genotype and Phenotype Combination of genes an organism has (actual gene makeup) – GENOTYPE Ex: TT, Tt, tt Physical appearance resulting from gene make-up – PHENOTYPE Ex: hitchhiker’s thumb or straight thumb

Genetics Vocabulary Review Choices: 1)YY 2)Tall 3)Yy 4)SS 5)yY 6)gg 7)Smooth 8)Green 9)TT 10)Dwarf Which choice(s) are examples of: Genotypes? 1, 3, 4, 5, 6, 9 Phenotypes? 2, 7, 8, 10 Homozygous genotypes? 1, 4, 6, 9 Heterozygous genotypes? 3, 5 Homozygous recessive genotypes? 6 Homozygous dominant genotypes? 1, 4, 9

Dominant vs. Recessive If Brown eye color is dominant over blue eye color, how would you indicate… –The brown allele? –The blue allele? #1

Dominant vs. Recessive If dimples in the cheeks are dominant, how would you indicate… –The allele for dimples? –The allele for no dimples? #2

Dominant vs. Recessive If left thumb over right thumb is dominant, how would you indicate… –Left over right? –Right over left? #3

Mendel laid the groundwork for genetics. Traits are distinguishing characteristics that are inherited. Genetics is the study of biological inheritance patterns and variation. Gregor Mendel showed that traits are inherited as discrete units. Many in Mendel’s day thought traits were blended.

Mendel’s data revealed patterns of inheritance. Mendel made three key decisions in his experiments. –use of purebred plants –control over breeding –observation of seven “either-or” traits

Mendel used pollen to fertilize selected pea plants. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. –P generation crossed to produce F 1 generation –interrupted the self-pollination process by removing male flower parts

Mendel allowed the resulting plants to self-pollinate. –Among the F 1 generation, all plants had purple flowers –F 1 plants are all heterozygous –Among the F 2 generation, some plants had purple flowers and some had white

Mendel’s Experiment

Each trait had a 3:1 ratio. No way that can be a coincidence!

Mendel’s Findings in Modern Terms If the two alleles of a particular gene present in an individual are the same, the individual is said to be homozygous. (dominant or recessive) If the alleles of a particular gene present in an individual are different, the individual is heterozygous. In heterozygous individuals, only the dominant allele is expressed; the recessive allele is present but unexpressed.

Mendel drew three important conclusions. –Traits are inherited as discrete units. –Organisms inherit two copies of each gene, one from each parent. –The two copies segregate during gamete formation. –The last two conclusions are called the law of segregation. purplewhite

Defined: Tools used to determine genetic probability Probability = likelihood that a certain event will happen 2 Steps: –1) Place parent genotypes on the outside of the box –2) Fill in the boxes Punnett Squares

Cross a homozygous dominant yellow (YY) plant with a homozygous recessive green (yy) plant Key Y = yellow y = green Probability of growing a yellow plant? _____________ Probability of growing a homozygous recessive plant? ____________ 100% 0% Probability of growing a homozygous dominant plant? ____________ 0%

Cross a heterozygous dominant yellow (Yy) plant with a heterozygous dominant yellow (Yy) plant Key Y = Yellow y = green Probability of growing a heterozygous plant? ________ Probability of growing a green plant? ________ Probability of growing pure yellow? _________ 50% 25% 25%

Maria is a heterozygous healthy (Hh) female and Jeff suffers from recessive cystic fibrosis (hh). Key H = healthy h = cystic fibrosis Probability of having a healthy child? _________ Probability of having a homozygous dominant child? ________ 50%0%

Autosomal Dominance Inheritance

What’s an Autosome? Autosome: refers to chromosomes 1-22 –E–Ex: Autosomal disorders: gene for the disease is found on chromosomes 1-22 Autosomal Recessive Inheritance –M–Must inherit two copies of the disorder to be affected –H–Healthy is dominant (HH or Hh) –D–Disease is recessive (hh) –E–Ex: Cystic fibrosis, PKU, Albinism, Sickle cell anemia Autosomal Dominance Inheritance –O–Only need to inherit one copy of the disorder to be affected –D–Disease is dominant (HH or Hh) –H–Healthy is recessive (hh) –E–Ex: Familial hypercholesterolemia (also called FH), Huntington’s disease, Neurofibromatosis

Autosomal Dominance Inheritance Disease is dominant (FF or Ff) –H–Homozygous dominant: early death and don’t survive to reproduce –H–Heterozygous live into adulthood Healthy is recessive (ff) ex: Paul has familial hypercholesterolemia and Stacy is healthy. The two have 3 children. After testing, the middle child is the only healthy child. Key F = FH disease f = healthy disease healthy PaulStacy Ff ff

Autosomal Dominance Inheritance Huntington’s disease is a dominant disorder found on chromosome 4. Betty and Marcus met at a support clinic they have been attending to help them cope with the knowledge of their illness with Huntington’s disease. They would like to know the risk of having a healthy child, now that Betty is pregnant. Key H = Huntington’s disease h = healthy diseasedisease diseasehealthy ? MarcusBetty Hh