genetics bad boys of genetics: patterns of inheritance which do not follow mendel’s rules

GENETICS

BAD BOYS OF GENETICS: PATTERNS OF INHERITANCE WHICH DO NOT FOLLOW MENDEL’S RULES

BIG IDEA Traits are inherited in a consistent pattern

OBJECTIVES Compare and contrast the patterns of

inheritance that do not follow Mendel’s rules. Explain how traits are influenced by the

environment.

INTRODUCTION PREDICT: What will be the result if you cross…

X

A RED SNAPDRAGON A WHITE SNAPDRAGON

INTRODUCTION

A PINK SNAPDRAGON!!!

INTRODUCTION BAD BOYS OF GENETICS

PATTERNS OF INHERITANCE WHICH DO NOT FOLLOW THE RULES ESTABLISHED BY MENDEL

These include… INCOMPLETE DOMINANCE CODOMINANCE POLYGENIC TRAITS MULTIPLE ALLELES ENVIRONMENTAL EFFECTS

INCOMPLETE DOMINANCESometimes called “Blended Traits” In organisms which follow complete dominance (or the rules set down by Mendel), the homozygous dominant (e.g. RR) and the heterozygous (e.g. Rr) would have the SAME PHENOTYPE

INCOMPLETE DOMINANCE: heterozygous individuals show phenotype that is in between the phenotypes of the two homozygous parents

INCOMPLETE DOMINANCE EXAMPLES

Snapdragons Red Flowering Plant x White Flowering Plant = PINK RR x rr = Rr

Cholesterol HH=can maintain healthy cholesterol levels Hh=cholesterol level 2x as high as normal (1 in 500 people) hh =cholesterol 5x as high (1 in million people) Called HYPERCHOLESTEROLEMIA Very serious condition, has even caused heart attacks in

two-year-old children

CODOMINANCE EXAMPLES

Palomino Creamy-golden horse with pale mane and tail Offspring of chestnut-colored horse and white horse

Roan cattle Roan cows have coats that are primarily red with

white hairs Offspring of red cows and white cows

CODOMINANCE CODOMINANCE: both alleles express

themselves fully, and both phenotypes are visible EXAMPLES

Chickens Black feathered chicken homozygous for black (BB) White birds also homozygous for white (WW) If you cross black and white bird…

BB x WW = BW Result is chicken with a pattern

of black and white feathers Same thing with Belted Galloways

or “OREO COWS”

Belted Galloways “ OREO COWS”

CODOMINANCE EXAMPLES

Human Blood Types Blood types refer to the two different proteins (ANTIGENS)

that coat the surface of red blood cells Type A blood type = type A protein Type B blood type = type B protein Type AB blood type = type A and B proteins Type O blood type = neither protein

POLYGENIC TRAITS POLYGENIC TRAITS: traits controlled by two or more

genes EXAMPLE

Eye Color is determined by genes for… TONE of pigment: color of pigment AMOUNT of pigment: blue eyes have less POSITION of pigment: eye pigment not distributed evenly,

creating patterns

MULTIPLE ALLELES So far, we have exclusively considered traits

with only two alleles for A PARTICULAR GENE Many traits have more than TWO alleles MULTIPLE ALLELES: traits which have 3 or

more alleles for that gene

MULTIPLE ALLELES Human Blood Type

Blood type is an example of codominance and MULTIPLE ALLELES

Blood types can be produced by 3 different alleles IA

IB

iPhenotype Genotype A IAIA or IAi B IBIB or IBi AB IAIB (codominance)

O ii Thus, there are 4 blood types controlled by 3 blood type alleles =

MULTIPLE ALLELES

ENVIRONMENTAL EFFECTS We have seen how many factors can influence

how a gene is expressed Genes are also influenced by ENVIRONMENT

(both internal and external) INTERNAL:

Different HORMONES in males and females produce different environment in your body, and thus affect genes

FEATHERS of birds (males are often brightly colored) HORNS of bighorn sheep (males are much heavier

and coiled)

ENVIRONMENTAL EFFECTS EXTERNAL

Hydrangeas: flowers BLUE in acidic soil, flowers PINK in neutral/somewhat basic soil

HIMALAYAN RABBIT Normally covered with WHITE fur and eyes/nose/feet are BLACK Extremities are COOLER than rest of body Body temperature affects expression of GENE that controls fur

color If fur removed and patch is kept cool, as the fur grows back it will

be BLACK

HUMAN HEIGHT: polygenic trait, also affected by nutrients in diet

Others: Butterflies: some species show darker wings if butterfly

born in spring, light in summer Japanese Goby fish: change sex back and forth

depending on presence of other fish and their sex

Sex-Linked TraitsPattern of inheritance is located on the X-chromosome or the Y- chromosome

Y is much smaller

Therefore, there are more X-linked disorders/traits

What numbers to you See?

Ex. Colorblindness

X-linked disorder

Most common in ?

Males (1/10)

Females (1/100)

X-linked Problems…

Hemophelia is a hereditary disease in which the blood does not clot. The allele for normal blood clotting is carried on the X chromosome.1. A carrier female marries a hemophilic man. How many male children will have hemophilia? How many female children?2. A normal woman whose father had hemophilia marries a normal man. What is the chance that their children will have hemophilia?3. Todd is not colorblind. He is married to Ann whose father was red-green colorblind. Todd and Ann have 2 children, Ed is colorblind and lisa is not. What are the genotypes of Todd, Ann, Ed, and Lisa?

1) One male child with hemophilia (25%) and one female child with hemophilia (25%).

2) There is a chance that one male child with have hemophilia (25%).

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