Genetics and Inheritance: Mendelian, Chromosomes, and Population Genetics

Mendelian inheritance

Pattern of inheritance discovered by Gregor Mendel showing how traits are passed from parents to offspring through discrete units called genes following predictable ratios like dominant and recessive inheritance

Chromosomes

Structures made of DNA and protein found in the nucleus that carry genetic information organized into genes

Somatic cells

Body cells that contain two sets of chromosomes one from each parent and are diploid

Sex cells

Reproductive cells sperm and egg that contain one set of chromosomes and are haploid

Recombination crossing over

Process during meiosis where homologous chromosomes exchange segments of DNA increasing genetic variation

Mitosis

Cell division that produces two identical diploid daughter cells used for growth and repair

Meiosis

Specialized cell division that produces four genetically unique haploid cells used for reproduction

Chromosomal mistakes

Errors such as nondisjunction where chromosomes fail to separate properly leading to conditions like trisomy

Mitochondrial DNA mtDNA

DNA found in mitochondria inherited only from the mother and useful for tracing maternal ancestry

Nuclear DNA nDNA

DNA found in the nucleus inherited from both parents containing most genetic information

Nitrogenous bases

Building blocks of DNA including adenine thymine cytosine and guanine that pair specifically

Proteins and amino acids

Proteins are large molecules made of amino acids that perform most functions in the body and are encoded by genes

Protein synthesis mRNA

Process where DNA is transcribed into messenger RNA which is then translated into a protein

Heritability

Measure of how much variation in a trait is due to genetic differences within a population

Genotype

Genetic makeup of an individual or the specific alleles they carry

Phenotype

Observable physical or physiological traits of an individual resulting from genotype and environment

Punnett square

Diagram used to predict the probability of offspring genotypes from parental allele combinations

Regulatory genes

Genes that control the expression of other genes turning them on or off

Lactose intolerance

Condition where adults cannot digest lactose due to reduced expression of the lactase gene

Dominance

Relationship where one allele masks the effect of another in a heterozygote

Recessive

Allele that is expressed only when two copies are present

Codominance

Situation where both alleles are fully expressed in a heterozygote such as AB blood type

Blood groups

Genetic systems that classify blood based on surface antigens on red blood cells

Locus

Specific location of a gene on a chromosome

ABO blood system

Blood type system with three alleles A B and O producing four phenotypes A B AB and O

Rhesus factor

Blood group system based on presence or absence of the Rh antigen positive or negative

Homozygote

Individual with two identical alleles for a gene

Heterozygote

Individual with two different alleles for a gene

CCR5Δ32

Genetic mutation that provides resistance to HIV infection by preventing the virus from entering cells

Gene expression

Process by which information from a gene is used to produce a functional product like a protein

Hardy Weinberg Equilibrium

Model stating that allele and genotype frequencies remain constant in a population if certain conditions are met

Hardy Weinberg conditions

No mutation random mating no natural selection extremely large population and no gene flow

Allele frequency

Proportion of a specific allele in a population calculated as number of that allele divided by total alleles

Genotype frequency

Proportion of individuals in a population with a specific genotype

Observed frequency

Actual measured frequency of genotypes in a population

Expected frequency

Frequency predicted by Hardy Weinberg equations based on allele frequencies

Hardy Weinberg equation

Mathematical model p squared plus 2pq plus q squared equals 1 representing genotype frequencies

P value

Frequency of the dominant allele in a population

Q value

Frequency of the recessive allele in a population

Calculating allele frequency

Count total alleles in population then divide number of specific alleles by total number

Importance of Hardy Weinberg

Provides baseline to detect evolution if population deviates from expected frequencies

Evolution in genetics

Change in allele frequencies in a population over time

Mutation

Random change in DNA sequence that introduces new genetic variation

Gene flow

Movement of alleles between populations through migration

Genetic drift

Random change in allele frequencies especially in small populations

Natural selection

Process where individuals with advantageous traits reproduce more successfully

Founder effect

Type of genetic drift when a small group starts a new population with limited variation

Bottleneck effect

Reduction in population size leading to loss of genetic variation

Polygenic traits

Traits controlled by multiple genes such as height and skin color

Environmental influence on phenotype

External factors like diet and climate that affect how genes are expressed

DNA structure

Double helix made of two strands of nucleotides held together by base pairing

Complementary base pairing

Adenine pairs with thymine and cytosine pairs with guanine ensuring accurate DNA replication

Replication

Process by which DNA makes a copy of itself before cell division

Transcription

Process where DNA is copied into messenger RNA

Translation

Process where mRNA is used to build a protein at the ribosome

Amino acid sequence importance

Order of amino acids determines protein shape and function

Gene mutation effects

Can be beneficial harmful or neutral depending on impact on protein function

Diploid

Having two sets of chromosomes typical of somatic cells

Haploid

Having one set of chromosomes typical of gametes

Karyotype

Visual display of chromosomes used to detect abnormalities

Nondisjunction

Failure of chromosomes to separate during meiosis leading to abnormal chromosome numbers