Genetic Inheritace

Important Vocab: GENES: factors that are passed on by parents to offspring that determine the inheritance of traits. Traits: a specific characteristic that varies from one individual to another. The different forms of a gene are called alleles(ah-le-eels).

Important Vocab (Continued) GENOTYPE – are the actual DNA coded genes or instructions that make you. PHENOTYPE – The express or what the genotype looks like in the physical world. For short – What you look like.

Gregor Mendel’s Peas Genetics is the scientific study of heredity. Gregor Mendel was an Austrian monk that studied the common garden pea and how various traits were inherited. Mendel is considered the Father of Genetics, because of his discovery of the basic rules of genetic inheritance and the inheritance pattern of simple dominance.

Genes and Dominance The principle of dominance states that some alleles are dominant and others are recessive. Dominant alleles – Only need one for this form to show in the phenotype Possible Genotype – (DD or Dd) Recessive – Need two alleles for this one to show in the phenotype Possible Genotype– (dd)

Segregation Principle of Segregation: During the formation of GAMETES (sex cells) – Alleles are separated (segregated) into different resulting daughter cells. **This is why some traits are some times said to skip a generation (recessive trait is hidden and then passed on)

Segregation Alleles separate during gamete formation. During gamete formation, alleles segregate from each other so that each gamete carries only a single copy of each gene. Each F1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness. The alleles are paired up again when gametes fuse during fertilization. The TT and Tt allele combinations produce tall pea plants; tt is the only allele combination that produces a short pea plant.

How genes work: For every gene you have 2 copies of that gene. - 1 from mom and 1 from dad. Since your mom and dad don’t necessarily have the same allele (version of the gene), there are different ways those two copies can interact. These different ways are called Inheritance Patterns.

Inheritance Patterns

Simple Dominance AKA – Mendelian Genetics Two alleles exist for the gene. One allele is Dominant One allele is recessive For the dominant phenotype to show through, you only need to inherit 1 dominant allele. For the recessive phenotype to show through, both of your alleles need to be recessive.

Simple Dominance

Incomplete Dominance Incomplete Dominance: neither allele is dominant but combine and display a new trait that is a mixing of the two alleles SYMBOLS USED Two capital letters, one with an apostrophe to indicate the different allele that is involved Ex. R (for the red allele) R’ (for the white allele) RESULT for Heterozygous - Blending of the two phenotypes (red + white = Pink)

Incomplete Dominance RR R’R’ RR’ RR’ RR RR’ R’R’

Codominance Codominance: both alleles of a gene are dominant and the heterozygous phenotype has both traits equally expressed SYMBOL: Two capital letters: Use the first letter of one trait (B for Brown) and the first letter of the other trait (W for White) RESULT of Heterozygous (BW) Spotty/blotchy NO BLENDING!

Codominance

Codominance

Let’s Stop and Think… Let’s say there are two alleles for the hair color trait- red and blue What would be the resulting phenotype of a heterozygous pair if the alleles showed codominance? A. Red B. Blue C. Purple D. Red and Blue patches

Multiple Alleles Multiple Alleles: the presence of more than two alleles for a genetic trait Blood Type Human blood type is governed by the presence of 3 different alleles: A B O However, each person only has 2 of these 3 alleles in their DNA

ABO Blood Type Blood types follow both Codominant and simple Dominant inheritance A and B are codominant A and B are both dominant over O SYMBOLS USED A allele = IA B Allele = IB O allele = i

Variation The following patterns use the three already describe in different combinations due to either having more than 2 alleles, multiple genes, or are located on the sex chromosomes.

Multiple Alleles: Blood Type

Let’s stop and think… What are the two allele combinations you can have for type A blood? IAIA and IAi What are the two allele combinations you can have for type B blood? IBIB and IBi

Let’s Stop and Think… What is the only allele combination you can have for type AB blood? IAIB What is the only allele combination you can have for type O blood? ii

Sex-Linked Traits genes which are carried only on the sex chromosomes ex: red green color blindness 2:25 males 1:150 females

Sex-Linked Traits DEFINITION: genes which are carried only on the sex chromosomes Traits are usually not seen in women because it can be masked by another dominant gene on the other X-chromosome Female – XBXb Male – XbY **Note – Guys only have 1 copy** EXAMPLE: Red – Green Color blindness

Color Blindness Test Can you see the letters and numbers in these squares?

Polygenic Traits In this pattern there are more than one gene responsible for a single trait Makes it possible for many types of genotypes and phenotypes Continuous variation EXAMPLES: Height, Body shape, Skin tone

Polygenic Example Skin Tone

Human Height Polygenic It’s often hard to tell where a person might get their height from (short lady is the tall lady’s mother)