Exam 2 Learning outcomes

Sex-linked characteristic

genes that are located on the sex chromosome

Sex-influenced characteristic

autosomal genes that are more readily expressed in one sex

Sex-limited characteristic

autosomal genes whose expression is limited to one sex

Phenocopy

the environment imitates genetics

Pleiotropy

one gene affects multiple different traits

Penetrance

the percentage of individuals with a particular genotype who actually show the phenotype

Genomic imprinting

Gene expression depends on which parent the allele came from.

Autosomal dominant

appears in every generation, males and females affected equally, affected person usually has an affected parent

Autosomal recessive

can skip generations, unaffected parents can have an affected child, males and females affected equally, often appears among siblings

X-linked recessive

more males affected

X-linked dominant

Affected father → All daughters affected because every daughter receives his x chromosome , Affected father → No sons because sons recieve his y chromosome

Mitochondrial

Affected mother → all children inherit it

Affected father → does not transmit it

Genetic maternal effect

Offspring inherit genes from both parents, but the nuclear genes of the mother determine the offspring’s phenotype

Mitochondrial inheritance

The hereditary determinants of a trait are extranuclear, and genetic transmission is only through the maternal cytoplasm

Amniocentesis

removes a sample of amniotic fluid from the uterus (can be used for DNA analysis and chromosome analysis)

Ultrasound

uses high-frequency sound waves to create a picture of the fetus

Chorionic Villus Sampling

removes a small sample of chorion which is part of the placenta

Maternal Blood Screening

examines substances in the mother’s blood

Noninvasive prenatal screening

NIPS uses maternal blood to examine fragments of fetal DNA (can screen for chromosome abnormalities - Down Syndrome, Trisomy 18, Trisomy 13)

Preimplantation Genetic Diagnosis

In vitro fertilization and genetic testing (a single cell can be removed from an early embryo and tested for genetic abnormality)

Why is recombination important for segregation?

During prophase 1, homologous chromosomes pair up to form a bivalent. Crossing over creates physical connections between homologs. These connections help the homologous chromosomes stay associated so they can separate during Meiosis I.

Explain how a specific combination of linked alleles (haplotype) can persist through many generations (linkage disequilibrium).

A haplotype is a particular combination of alleles that occurs together on one chromosome. This is related to linkage disequilibrium: certain allele combinations occur together more often than expected by chance.

Physical Distance

The actual amount of DNA between two genes.

Genetic distance

based on how frequently crossing over occurs between the genes

Why is there a difference between physical distance and genetic distance?

Crossing over doesn’t happen equally throughout a chromosome. Some regions have lots of recombination, while others have very little.

Illustrate the steps of meiosis and describe the particular stage of meiosis that leads to genetic variation in offspring.

Independent Assortment - During metaphase I, homologous pairs can line up in different orientations. That means different combinations of maternal and paternal chromosomes can enter the gametes. Crossing over - During prophase, homologous chromosomes exchange DNA. This creates recombinant chromosomes.

Describe how a "lod" score is used as evidence for gene linkage in humans.

It is used to determine whether two genes are likely to be linked in humans. A positive/high LOD score supports linkage. A negative LOD score argues against linkage.

Recombination hotspots

Regions where crossing over happens more frequently.

Low- recombination regions

Regions where crossing over happens less frequently.

SNP (Single Nucleotide Polymorphism)

A difference at one nucleotide/base in the DNA sequence

CNV (Copy Number Variant)

A section of DNA is present in different numbers of copies among individuals.

Explain how SNPs can be used as genetic markers even if they do not cause phenotypic changes.

If a SNP is located close to a disease-causing gene, the SNP and disease gene are likely to be inherited together because they are linked.

Differentiate between a gene and an allele, including the recognition that genes may have many alleles.

A gene is a segment of DNA associated with a particular biological function or trait. An allele is one or two more alternative versions of a gene

Explain the main purpose of genome-wide association studies (GWAS), discussing how GWAS data can be used to inform scientists and physicians about genetic diseases.

The purpose of GWAS is to look across the genome for genetic variants that are associated with a particular trait or disease. Researchers can compare genetic information from people with a disease to people without a disease.

sGRNA

guides the Cas-9 and finds the target DNA

cRNA

contains the sequence that allows the CRISPR system to recognize and target DNA

tracrRNA

helps form the guide RNA structure and interact w/ Cas-9

seed sequence

Helps determine whether the guide RNA correctly matches the target

PAM

part of the target DNA, required DNA sequence next to the target