Biology Exam 7

Phenotype:

EX:

Physical Form of a trait.

Phenotype (Brown fur)

Genotype:

EX:

Alleles for a Trait. Genotype (Bb)

Segregation:

Separation of alleles into gametes

Diploid:

Having both maternal and paternal copies of a chromosome 

Haploid:

Having one copy (mother OR father) of each chromosome 

Dominant Allele:

\-What can they do?

Expressed in heterozygotes. *Can mask the presence of recessive traits.*

Recessive Allele:

Hidden in heterozygotes. Does not produce a trait at all when only one copy is present. 

Allele:

Code for the same trait, but have different forms of a gene.

How many alleles do diploid cells have?

Diploid individuals have 2 genes/alleles for every trait, though more than 2 alleles may exist.

What happens in multiple allelism:

No matter how many alleles for a trait are present in the population, each individual can only have two of the alleles - one from each parent.

Homozygous:

EX:

Same alleles.

Homozygous (BB or bb) 

Heterozygous:

EX:

Different alleles. Heterozygous (Bb)

**Mendelian Genetics:**

Studies inheritance of traits 

What does mendelian genetics display?

Shows traits are passed on as discrete units from parent to offspring vs previous “blending” idea. 

What did Mendel study?

Studied 7 non-linked traits of garden pea plants 

**True-breeding** Parents:

Are parents that always have offspring with the same trait. 

What are the true-breeding parents referred to?

The parents are called the **P (parental)** generation.

What are the offspring of true-breeding parents referred to as?

The offspring of the parental cross are called the **F1** generation.

What happens when you cross F1 generation to eachother?

Crossing them to each other, produces **F2** plants. 

basic ratio when you have a dihybrid cross with 2 heterozygotes:

* 9/16 are dominant for both traits 
* 3/16 are dominant for 1 traits, recessive for the other
* 3/16 are recessive for 1 trait, but dominant for the other 
* 1/16 are recessive both both traits 

**Alternative Patterns of Inheritance we will be discussing.**

\

A. Incomplete Dominance

B. Epistasis

C. Polygenic Inheritance

D. Pleiotropy

E. Multiple Alleles and Codominance

F. Sex-Linked Traits

G. Dominant Defects

**Incomplete Dominance:**

Both alleles are expressed in the heterozygote to give an intermediate phenotype, where both of them are expressed. 

Incomplete Dominance punnet characteristic:

You would only use capitals when making the punnett square for these problems. 

Incomplete Dominance Examples:

* Roan livestock. RR= red, WW=white, RW= roan
* Many pink flowers.
* Wavy hair. SS=straight, CC=curly, SC=wavy
* Yellow-green seedlings

How are pink flowers made?

A cross between red and white flower plants results in offspring with pink flowers

**Epistasis:**-Where is it commonly seen?

One set of genes suppresses expression of another (often coloring genes in animals, plants, and hair color).

Epistasis. Phenotype characteristics:

Always has 3 phenotypes

What must you do to all ratios?

ratios always have to be simplified! 

**Polygenic Inheritance:**

When __many__ genes influence one trait (most traits!) 

Polygenic Inheritance.

Ex:

Eye color, hair color, height. 

How can you tell if a trait is polygenic and why?

Can tell when a trait is polygenic when there is **continuous variation** in phenotype since so many genes contribute. 

What variation is shown when a few genes are present?

Traits due to one or two genes show **discontinuous variation** = just a few phenotypes 

**Pleiotrophy:**

When one gene influences many traits 

Pleiotrophy Ex:

SRY Gene

What does the SRY gene do?

\-What happens when it’s mutated?

SRY Gene starts testis development. Mutation will cause females to develop male characteristics. 

**Carrier:**

Heterozygote who has one copy of a recessive allele (don’t have the disease), typically doesn’t know they have it

What is the term carrier only used for?

Used in reference to disease genes only. EX: not I am a carrier for blue eyes. 

**Diseases Caused By Autosomal Recessive Alleles:**

PKU

albinism 

cystic fibrosis

Tay Sachs Disease

Sickle cell anemia

Xeroderma pigmentosum

What do Autosomal Recessive Alleles mean?

someone could be a carrier

Albinism:

Can’t make any pigment.

Multiple Alleles and Codominance Ex:

**Human ABO blood types** 

What are the blood type alleles?

IA= A antigen

IB= B antigen

i= No antigen 

How many blood type alleles do humans have?

Everyone has 2 of these 3 alleles (1 from each parent). 

What part of ABO blood type is codominant and why?

IA and IB are **Codominant**- Equally expressed in heterozygotes. 

A and B are _______ to what?

A and B are dominant to the i allele.

What do the alleles in blood do?

The alleles code for **Antigens**

**Antigens**:

Proteins on the surface of cells (glycoproteins or rbc’s)

**Antibody:**

Protein in the blood that destroys foreign antigens, gives long-lasting immunity. 

How do antibodies give immunity?

We make antibodies against antigens our cells don’t have-perceived as foreign 

Blood Type-A

Genotype(s):

Antigens:

Antibodies:

\-IAIA (homozygous) or IAi (heterozygous, has one of the recessive I alleles)

\- A

\-Anti-B

Blood Type-B

Genotype(s): 

Antigens: 

Antibodies: 

* IBIB or IBi
* B
* Anti-A

Blood Type-AB

Genotype(s): 

Antigens: 

Antibodies: 

* IAIB (codominant)
* A and B
* None. Universal recipient

Blood Type- O

Genotype(s): 

Antigens: 

Antibodies: 

* ii
* None
* Anti-A and Anti-B. Universal donor

If a black chicken is crossed with a white chicken and the offspring are black and white checkered, this is an example of:

Codominance b/c both colors are expressed.

If a black horse mated with a white horse and their foal was grey, this is an example of:

Incomplete Dominance

Rh Blood Types (rhesus factor):

Another antigen on the surface of RBC’s. 

Rh blood type. Phenotypes:

Rh+ (dominant)           

rh-

RG blood type genotype:

* RR (homozygous) or Rr (heterozygous)
* rr (recessive allele, means you are homozygous)

What is the problem with Rh blood type?

There are problems resulting from an rh- mother carrying an Rh+ baby.

Why is an rh- mother with Rh+ baby bad?

Because mother makes antibodies against the baby’s antigens, at birth problems arise.  

**Sex-Linked Traits:**

Alleles are carried on the X chromosome., most are recessive. 

Sex-Linked Traits alleles characteristics:

Alleles for X-linked traits are shown as a superscript over the letter X.

Sex-Linked Traits ratio characteristics:

MUST give m/f ration separately

Sex-Linked Traits Ex:

* Red-Green color blindness
* Duchenne’s muscular dystrophy: Fatal muscle deterioration, starts in childhood
* Hemophilia: bleeders disease 

Why is sex chromosomes unusual?

Sex chromosomes are unusual homologues, X is so much bigger than the Y chromosome. 

What gender is most likely to show these traits?

Males are much more likely to show these traits

Why are males more likely to show these characteristics?

Since males only have one X chromosome (one x alllele), having just one recessive gene gives the trait (express).  

Hemophilia genotypes:

* XhY = male w/hemophilia 
* XHXh = unaffected carrier female 
* XhXh = Female with hemophilia 

What are males to X-linked traits and why?

Males are __hemizygous__ for X-linked traits = only have one copy.

What can’t we call males and why?

Can’t call a male homo or heterozygous for a trait because it implies they have 2 alleles, they only have one on X. 

**How are sex-linked traits generally transmitted between generations?**

From carrier mother to son (dads give their Y to sons). 

Can there be hemophilic/color-blind etc. Females?

\- Could be born to a carrier mother and an affected father

With any sex-linked recessive trait, what must affected females (EX: xhxh) always have and why?

Have to have affected fathers (dads have to give daughters one of their recessive x’s). 

**Dominant Gene Abnormalities:**

Parents have a 50% chance of passing these traits onto their  offspring.

In dominant gene abnormalities why do parents have a 50% chance of passing traits onto offspring?

Those with dominant diseases are generally always heterozygous for that disease.  It only takes one copy of the dominant allele to cause the genetic disease.

How can offspring be homozygous for a dominant linked disease?

Only way for a child to be homozygous for a dominant linked disease is for both parents to have the disease = exceedingly rare 

dominant linked disease Ex:

* Huntington’s Chorea
* Polydactyly (extra digits)
* Marfan’s Syndrome

Huntington’s Chorea characteristics:

* Late onset (after 35)  


* Jerking
* twitching
* mental decline
* fatal withinin 15 yrs of onset

Pedigree:

A family tree showing the transmission of the genetic traits between generations.

Pedigree.

What do horizontal lines indicate?

Horizontal lines between people indicate that they had offspring together.

Pedigree.

\-What do vertical lines indicate?

Vertical lines indicate a child born from a relationship.

Pedigree.

\-How are generations drawn?

Each generation is drawn in a parallel row.

Pedigree.

\-How are men and women represented?

In pedigrees, men are represented by squares, and women are represented by circles.

Pedigree.

How are traits represented?

When following a genetic trait, the circles or squares are filled in to indicate individuals who have the trait, half filled=carrier.

Autosomal Recessive Trait:

Autosomal recessive traits carried on autosomes pass from both parents onto their child.

Autosomal Recessive Trait Characteristics:

* Males and females are equally likely to be affected 
* Affected offspring often have unaffected parents 
* Unaffected parents of affected offspring are heterozygous (carriers) 
* Affected offspring are homozygous 
* Won’t appear for every generation, maybe yes, maybe no. 

For an autosomal recessive trait, affected individuals are homozygous recessive.

True

For an autosomal recessive disease, how can two unaffected individuals have an affected child?

* Both parents are carriers.
* Both parents are heterozygous.

Autosomal Dominant Trait Characteristics:

* No unaffected carriers 
* Mother and father are equally likely to be affected
* Affected offspring have atleast one affected parent 
* Affected offspring are heterozygous if only one parent is affected 
* Unaffected offspring are homozygous recessive 
* If one parent is heterogygous, about ½ of the offspring will be affected
* Trait does not skip generations 

PIC: Autosomal Dominant Trait Pedigree 

For an autosomal dominant disease, unaffected individuals are homozygous recessive.

True

For an autosomal dominant inherited disorder, why can't two unaffected people have an affected child?

* Neither of the parents have the disease-causing allele.
* Both parents are homozygous recessive. 

X-linked recessive trait characteristics:

* Males are affected more frequently than females 
* Trait is never passed from father to son
* Affected sons are usually born to carrier mothers 
* About ½ of the sons of a carrier mother will be affected 
* All daughters of affected males and unaffected non-carrier females are carriers 
* Trait often skips generations

PIC: X-linked recessive trait pedigree

**Linked Genes:**

Genes found on the same chromosome. 

How are linked genes different from sex-linked genes?

Sex-linked Genes refers to a gene that is on the X chromosome. 

Crossing over increases the number of possible gamete combinations for linked genes.

True. 

Linked genes characteristics:

* Don’t follow the principle of independent assortment, but are often passed on together. 
* The closer together two genes are on a chromosome, the less likely they will assort independently.
* As the distance between 2 genes increases, the probability of crossover between them increases

Why are genes less likely to go through independent assortment the closer they are together?

This is because a crossover is less likely to happen between them, making it more likely that they will stay linked