1. Patterns of inheritance
Chapter 10
Patterns of inheritance

2. 10.1 Chromosomes are packets of genetic information
Terms to review
Gene- portion of a dna that codes for a protein or RNA
Alleles- versions of a gene
Chromosomes- molecule of DNA and associated proteins
Diploid cell- complete set of chromosomes
Autosomes- chromosomes that do not determine gender
Sex chromosomes- determine gender (XX or XY)
Homologous pair- chromosomes with matching genes
Fertilization- two gametes fuse creating a zygote

3. 10.2 Mendel’s experiments uncovered basic laws of inheritance.
Mendel used pea plants to study inheritance.
He found that dominant alleles mask recessive alleles.
The only way a recessive trait shows up is if two recessive alleles are inherited.
For each gene, a cells two alleles may be identical or different.

4. A genotype is the combination of alleles inherited.
Homozygous means two identical alleles were inherited(either dominant or recessive)
Heterozygous means one of each type was inherited.
Phenotype is the organisms appearance or observable characteristics.
Wild-type allele, phenotype, or genotype is the most common form or expression of a gene in a population.
Mutant allele, phenotype, or genotype is a variant that arises when a gene undergoes a mutation.

5. Every generation has a name:
P generation- parental
F1 is the first filial generation- offspring of P generation
F2 is the offspring of the F1 generation.

6. Chapter 10
Section 3

7. A. Monohybrid crosses track the inheritance of one gene
Mendel discovered that when two organisms that are heterozygous for a trait are crossed, they exhibit both phenotypes in a 3:1 ratio, dominant to recessive.
A monohybrid cross looks at one trait only.
A punnett square is a diagram used to show alleles combinations that offspring may inherit.

8. A test cross is used to show if the genotype of a dominant phenotype is heterozygous or homozygous recessive.
The organism with the unknown phenotype is crossed with a homozygous recessive mate.

9. B. Meiosis explains Mendel’s Law of segregation
Not only did Mendel discover alleles, he also deduced the Law of Segregation.
This law states that the two alleles of each gene are packaged into separate gametes. They segregate or move apart from each other during gamete formation.
This principle applies to all diploid species.
Punnett squares show probabilities.

10. 10.4 Genes on Different chromosomes are inherited independently
A. dihybrid crosses track the inheritance of two genes at once.
Mendel wondered if traits influenced the inheritance of other traits. He set up dihybrid crosses to test this.
A dihybrid cross is a mating between two individuals that are heterozygous for two genes.
The four genotypes possible occur in a ratio of 9:3:3:1

11. B. Meiosis explains Mendel’s law of independent assortment
Law of independent assortment states that during gamete formation, the segregation of the alleles for one gene does not influence the alleles for another gene(if the genes are on separate chromosomes)
The alleles are randomly packaged into gametes with respect to each other.

12. Punnett squares for more than two traits are very large.
An easier way to predict genotypes and phenotypes is to use the product rule.
This states that the chance that two independent events will both occur equals the product of the individual chances that each event will occur.

13. 10.5 Genes on the same chromosome may be inherited together
A. Genes on the same chromosome are linked.
Linked genes are genes that are carried on the same chromosome, so they are inherited together.
They do not assort independently
First noticed by Bateson and Punnett when they observed different ratios than predicted by Mendel’s laws.

14. Thomas Hunt Morgan found the same type of patterns in fruit flies
Thomas Hunt Morgan found the same type of patterns in fruit flies. He found four linkage groups(collections of genes inherited together).
Each linkage group was simply a set of genes transmitted together on the same chromosome.
Sometimes, the scientists would see gene combinations that were not present in either parent. This is because of crossing over that occurs during meiosis.
Offspring either inherit a parental chromatid or a recombinant chromatid.

15. B. Studies of linked genes have yielded chromosome maps
Sturtevant found that the closer together two genes are on a chromosome, the less likely they are to be separated by crossing over. The further apart, the more likely to be separated.
This led to create linkage maps which are diagrams of gene order and spacing on chromosomes.

16. Phenotypes were once used to make linkage maps, but now gene markers are used. These are valuable for showing probability of inheriting certain genetic disorders.

17. 10.6 Gene expression can appear to alter Mendelian ratios
A. Incomplete dominance and co-dominance
Mendel studied complete dominance but sometimes the heterozygous offspring do not have the trait of either parent.
Examples- incomplete dominance- heterozygous has a third phenotype that is intermediate. It looks like a blending of traits.

19. Co-dominance- two different alleles are expressed together in the phenotype.
Example- blood types and roan fur color

21. B. Some patterns are difficult to interpret
Pleiotropy- one gene has multiple effects on the phenotype. This happens when one protein is important in different biochemical pathways or affects more than one body part or process.
Example- Marfan Syndrome and porphyrin

22. Ex. Blood clotting, porphyra
Protein interactions- Many proteins can interact to contribute to a single phenotype. This complicates the analysis of inheritance patterns.
Ex. Blood clotting, porphyra
Epistasis- when one genes product affects the expression of another gene.
Example- male pattern baldness, and inconsistencies in ABO blood type patterns.

23. 10.7 Sex linked genes have unique inheritance patterns
A. X and Y chromosomes determine sex in humans
XX is female
XY is male
The y chromosome plays the biggest part in human sex determination.
An embryo that has a working copy of the SRY gene develops into a male because the gene encodes a protein that switches on genes that direct the testes to produce testosterone. Other reactions are also switched on. SRY also turns on a gene encoding a protein that dismantles female structures.

24. The Y chromosome has fewer than 100 genes so there are very few Y linked disorders- most involve defects in sperm production.

25. B. X-linked recessive disorders affect more males than females
The X chromosome carries more than 1000 protein coding genes. Therefore most sex linked traits are X-linked.
More males show X-linked traits because the Y chromosome does not have a corresponding gene to “mask” the gene from the X chromosome.
Most X-linked traits are caused by recessive alleles. Females can only show the trait if they have two recessive alleles. The male shows the trait whether it is recessive or dominant.

26. C. X inactivation prevents “double dosing” of proteins
Since female cells have two X chromosomes, they have a double dose of proteins that are coded for on the X chromosome.
One X chromosome is inactivated at random in each cell.
This is why females who are heterozygous for an X linked disorder will have less severe symptoms than a male.

27. 10.8 Pedigrees show modes of inheritance
Pedigrees are diagrams used to show the passing down of traits through generations for autosomal dominant and autosomal recessive traits. Heterozygous individuals are “carriers” for the trait.
X-linked recessive conditions show unique patterns of inheritance.
Pedigrees can be difficult to construct for many reasons.

30. 10.9 most traits are influenced by the environment and multiple genes
A. The environment can alter phenotypes-
External environment can profoundly affect gene expression
Fetal alcohol syndrome, fur color pattern in Siamese cats, depression, type II diabetes.

31. B. Polygenic traits can alter the phenotype
Polygenic- phenotype reflects the activities of more than one gene.
Ex. Eye color, skin color
Sometimes environment can also influence a polygenic trait. Ex. Height, body weight, skin color, intelligence.