IB Bio Unit 6 Genetics
What is the Chi-square test?
Checks whether a distribution is significantly different than an expected or theoretical distribution
When do recombinants in linked genes form?
Crossing over (increases genetic variation) -Occurs a few and rarely
What is alleles?
Different versions of a gene
What is a genetic disease?
Diseases caused by an altered gene/sets of gene
When do alleles segregate?
During the formation of gametes (meiosis, anaphase I)
What cells are haploid?
Sex cells (gametes) -1 copy of each chromosome
What is a genotype?
The combination of alleles
What is a phenotype?
The expression of alleles (physical appearance)
Why are most sex-linked traits X-linked?
There are more genes on the X chromosome and it is found in both male and female
What is a recessive allele?
An allele that is masked when a dominant allele is present
What cells are diploid?
Body cells -2 copies of each chromosome
What is a linked gene?
-A group of genes whose loci are all on the same chromosome and inherited together during meiosis (no individual assortment) -B/c they are linked, linked-genes show monohybrid inheritance patterns -Does NOT conform to normal Mendelian ratios of a dihybrid cross
What two questions should you ask yourself when determining the mode of inheritance in a pedigree?
-Do you see a trait skipping a generation? (if yes, it is recessive) -Are more males affected than females? (if yes, it is sex-linked)
Why do sex-linked traits exhibit different patterns of inheritance?
-Females cannot express Y-linked traits (lack Y chromosome) -Males cannot mask X-linked recessive traits
What is codominance?
-Heterozygote with showing both alleles -AB blood type
Why are genetic disease rare in humans?
-It is unlikely that one parent will have a mutation on a disease relate gene -Very few disorder are controlled by dominant mutant alleles (recessive ones don't show if you inherit just one copy)
3 fundamental rules established after Mendel's observations
-Law of Segregation: Alleles are separated when haploid gametes form -Law of Independent Assortment: Separation of alleles for one gene occurs independently of the separation of alleles for any other given gene -Principle of Dominance: Recessive alleles will be masked by dominant alleles
What are illnesses caused by dominant alleles?
-One allele (H=diseased, h=normal) affect phenotype over the other version -Huntington's disease
What are illness caused by recessive alleles?
-One allele (h=diseased, H=normal) affect phenotype over the other version -Cystic fibrosis
What are new combinations of traits different from those shown in the parent line are called?
-Recombinant
What are illness caused by co-dominant alleles?
-Two dominant alleles that both adds to phenotype -Sickle cells
What is test cross?
-Used to determine the genotype of an unknown individual -The unknown is always crossed with a known *homozygous recessive*
What are illnesses by sex linked genes?
-X-linked recessive conditions -Hemophilia -Color blindness
What is a sex-linked gene?
A gene located on either sex chromosome (X or Y)
What is Mendel's Law of Independent Assortment?
-when two or more characteristics are inherited, individual hereditary factors *assort independently* during gamete production, giving different traits an equal opportunity of occurring together
What is the phenotype ratio of dihybrid test cross?
1:1:1:1
What is the phenotype ratio of dihybrid cross?
9:3:3:1
What is a monohybrid cross?
A cross between individuals heterozygous for a single character
What is a dominant allele?
A form of a gene that is fully expressed, even when two different alleles are present
What is the antigen and antibody for blood type A?
Antigen: Antigen A Antibody: Anti-B Antibody -Cannot have B or AB blood -Can have A or O blood
What is the antigen and antibody for blood type AB?
Antigen: Antigen A and B Antibody: None -Can have any type of blood
What is the antigen and antibody for blood type B?
Antigen: Antigen B Antibody: Anti-A -Can have B or O blood -Cannot have A or AB blood
What is the antigen and antibody for blood type O?
Antigen: None Antibody: Anti-A, Anti-B Antibody -Can only have O blood
What is a mutagen?
Anything that causes a change in the DNA sequence Ex: X- Rays, UV radiation, radioactive substances
What is homozygous dominant?
Having two copies of the same dominant allele ex. AA
What is homozygous recessive?
Having two copies of the same recessive allele -recessive alleles are only expressed when *homozygous*
What is heterozygous?
Having two different alleles for a particular gene (dominant allele is expressed)
Genotype of blood type A
IAIA or IAi
Genotype of blood type AB
IAIB
Genotype of blood type B
IBIB or IBi
What is gene locus?
Location of a gene on a chromosome
What is codominant?
Pairs of alleles which are both expressed when present
How to determine whether a gene is linked or unlinked
Unlinked: form *all* phenotypic combinations via random assortment Linked: only produce recombinant phenotypes when crossing over occurs (occurs at low frequencies)
Genotype for normal females (sex linkage)
XN XN
Genotype for carrier females (sex linkage)
XN Xn
Genotype for normal males (sex linkage)
XN Y
Genotype for affected females (sex linkage)
Xn Xn
Genotype for affected males (sex linkage)
Xn Y
Genotype of blood type O
ii