Bio Chap 9 Pop Quiz Preparation
Bio Chap 9 Study Guide
Finn Ryan
Chapter 9, pp. 165-181 - Sections 9.8-9.23
Non-Mendelian Genetics
9.8- Family Pedigrees
Geneticists can’t perform test crosses on people, so they must analyze the previous results
Pedigree- Family tree for the history of a given trait
9.9- Inheritance of 1 trait can be controlled by 1 gene
Mutant trait- a trait (can be dominant or recessive) that is less common in nature
Carriers- Carry a recessive or dominant allele
Different disorders are dominant or recessive (there’s a table of them on pg 166)
Cystic Fibrosis- most common genetic disorder, recessive
Achondroplasia- Serious genetic disorder, dominant
Dominant disease alleles cause less death than recessive alleles because dominant alleles kill the carrier and that’s the end
Huntington’s disease- Degenerative disorder of the nervous system that usually doesn’t appear until age 35-45
Allele for Huntington’s disease is dominant, so anyone inheriting dies
This shows dominant allele is not necessarily “better”
9.10- New Technology
Genetic screening informs decisions about family planning and are available for dominant diseases
Amniocentesis- Physician inserts a needle through abdomen into mother’s uterus and extracts 20 ml of of amniotic fluid (bathes developing fetus)
The extracted cells are grown in a lab for a few weeks
The resulting karyotyping can detect chromosomal abnormalities like down syndrome
Performed between 14-16 weeks pregnant
Chorionic villus sampling (CVS)- Physician extracts part of chorionic villus tissue from placenta
Inserts a tube through vagina and cervix into uterus
Results of karyotyping can be viewed in 24hrs
Performed between 8-12 weeks pregnant
Both tests cause risk of complications (CVS has a bigger miscarriage risk)
Ultrasound imaging- uses sound waves to produce a picture of the fetus
9.11- Incomplete dominance
Complete dominance- dominant allele has same phenotypic effect whether in one or two copies
Incomplete dominance- Appearance of F1 hybrids falls in between the phenotypes of the two parental varieties
EX: Red flower x White flower = 4x Pink flower
9.12- Many codominant alleles
ABO blood group phenotype in humans- involves three alleles of a single gene called Ia Ib and i
Various combinations of these alleles can produce 4x different phenotypes: Type A, B, AB, or O
Ia and Ib alleles are codominant, both expressed in type AB blood
Codominant- Both alleles are expressed in heterozygous individuals
Make sure to distinguish between codominance and incomplete dominance
If Maria has type O blood and her sister has AB blood their father has genotype Ib i and their mother has genotype Ib i
9.13- Single gene affects multiple things
Pleiotropy- One gene influences multiple characteristics
Pleiotropy example: Sickle-cell disease
Makes red blood cells produce abnormal hemoglobin that clumps together
As hemoglobin crystalizes the normal disk shaped red blood cells become sickle shaped with jagged edges
Sickle cells get destroyed immediately and lower red blood cells
Sometimes heterozygotes for sickle cells still get it if their blood’s oxygen is reduced (at high elevation etc.)
Heterozygote displays incomplete dominance for trait
At molecular level sickle cell is codominant because heterozygotes can have some sickle cells and some regular cells
9.14- Many genes can make a characteristic
Polygenic inheritance- additive effects of ≥2 genes on a single phenotypic character
If a dominant trait = 1 UNIT of that trait (ex: skin color) then AaBcCc (moderately dark skin) is the same as aaBBCc
9.15- Environment affects characters
Things like sun exposure and culture can affect your appearance
9.16- Chromosome behavior agrees with Mendel’s laws
Chromosome theory of inheritance-genes occupy specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment during meiosis
Thus it is behavior of chromosomes during meiosis + fertilization that accounts for inheritance patterns
Law of independent assortment = orientation of homologous chromosome pairs in Metaphase I
Law of segregation = the separation of homologous chromosomes in anaphase I
9.17- Genes on the same chromosomes
Linked genes- Genes close to each other on the chromosome and tend to be inherited together
Sweet pea genes for flower color and pollen shape are on the same chromosome so meiosis in the heterozygotes led to mostly PL and pl instead of all four genotypes being equal
9.18- Crossing over
Recombinant chromosomes- carry DNA from two different parents
Often have different gene combos from parent chromosomes
Wild-type- the traits most common in nature(nothing to do w/ dominance)
Mutant- Traits that are less common (can be dominant or recessive)
Recombination frequency- percentage of recombinant offspring among the total
Crossovers break lineages and form recombinant chromosomes
9.19- People use crossover data to map genes
Genetic map- ordered list of the genetic loci along a chromosome
Linkage map- Genetic map based on recombinant frequencies
9.20- Chromosomes determine sex
Sex chromosomes- Designated X and Y that determine an individual’s sex
XY= Male XX=Female
After meiosis each gamete has one sex chromosomes and a haploid set of autosomes (22 for humans)
9.21- The inheritance of sex linked genes
Sex-linked gene- Single gene located on either sex chromosome
Majority of sex-linked genes are X-linked genes
9.22- Sex linked disorders affect mainly males
When a man inherits only one X linked recessive allele from his mother and it is a disease he automatically has it but women need two recessive X linked alleles (way rarer)
Hemophilia plagued the royal families of Europe (Czar Nicholas II of Russia had a kid, Alexis, w/ Hemophilia)
9.23- Y Chromosome explains evolution
Y chromosome is good for tracing past because it usually passes intact from father to son forming unbroken chain of male lineage
Read Chapter 13, pp. 268-271 - Sections 13.8-13.11 (Evolution of Populations)
13.8- Mutation and sexual reproduction makes genetic variation
Mutation- a change in the genetic information encoded in the nucleotide sequence of the DNA
Original source of genetic variation
13.9- Evolution happens in populations
Population- group of individuals of the same species that live in the same area and can potentially interbreed
Gene pool- consists of all copies of every type of allele at every locus in all members of the population
Microevolution- When the relative frequencies of alleles in a population change over a number of generations, evolution is occurring on its smallest scale
13.10- Hardy-Weinberg equation
Hardy Weinberg equilibrium- Way to detect microevolution
In Hardy-Weinberg equilibrium:
Allele frequencies in a population will not change from generation to generation.
If the allele frequencies in a population with two alleles at a locus are p and q,
then the expected genotype frequencies are p2, 2pq, and q2
Note that p+q=1 when p and q are representing allele frequencies
If you follow the frequencies of the alleles from generation to generation they won’t change in hardy weinberg equilibrium
Assumptions for staying in Hardy Weinberg Equilibrium:
Very large population
No gene flow between populations
When people move in and out of a population they disrupt
No mutations
Changing alleles or deleting genes modifies gene pool
Random mating
Individuals can’t mate preferentially
No natural selection
Natural selection alters allele frequencies
These 5 assumptions are rarely met in real populations
Since mutations are rare their effect on allele and genotype frequencies from one generation to the next is likely to be small.
13.11- When is Hardy Weinberg equation useful
Scientists use it to estimate how many people have alleles for inherited diseases
Important for dealing with genetic diseases