Chapters 12-15

What determines biological sex?

-sex hormones produced by gonads (ovaries in females, testes in males)

-Males produce higher levels of testosterone

-Females produce higher levels of estrogen.

-In a fetus, sex hormones shape development of sexual anatomy

-Sex hormone production depends on the set of chromosomes the fetus receives from parents

Gonads

produces sex hormones, ovaries in females and testes in males

Autosomes

22 of 23 pair of human chromosomes are autosomes

Sex chromosomes

23rd pair of human chromosomes

absence of a Y

a fetus will develop into a female

Sons’ inheritance

inherit one Y chromosome from the father and one X chromosome from the mother.

Daughters’ inheritance

inherit one X chromosome from the mother and one X chromosome from the father

SRY gene

on the Y chromosome, signals the testes to develop, testes produce testosterone

Sex isn’t always __

clear cut; there are genetic, hormonal, anatomical, and behavioral aspects to sex; each year, approximately 1 in 1500 babies in the United States fall into the category of “intersex.”

Colorblindness

Red-green color blindness affects approximately 7% of the male population in the US, but only approximately 0.4 % of women

Hemophilia

a blood clotting disorder that afflicts 1 in 5000 boys worldwide, but rarely afflicts girls

X linked trait

a phenotype that is determined by the allele on an X chromosome.

-Ex: DMD Duchenne muscular dystrophy is X linked and affects mostly males. If a mother has a DMD allele: the mother passes one of her two X chromosomes to each of her children. If a father has a DMD allele: the father passes his only X chromosome to his daughters and his only Y chromosome to his sons.

Recessive X linked trait

normal copy on one X chromosome masks the recessive disease allele on the other X chromosome.

Pedigree

visual representation of the occurrence of phenotypes across generations. Use to follow inheritance patterns. Boys have only one X chromosome and have a higher probability of inheriting X-linked diseases than girls

Y chromosome

sons inherit the Y chromosome from their fathers. Y chromosomes are very small and contain few genes.

Incomplete dominance

-a form of inheritance in which heterozygotes have a phenotype that is intermediate between homozygous dominant and homozygous recessive.

-shown when one allele doesn’t completely mask the presence of another allele

-there is a measurable effect on the phenotype of having one versus two copies of the dominant allele

Codominance

A form of inheritance in which the effects of both alleles are displayed in the phenotype of a heterozygote

-both maternal and paternal alleles contribute equally and separately to the phenotype.

-Example: ABO blood type. 3 blood group alleles A, B, and O. Possible genotypes are combinations of these three alleles: AA, AO, BB, BO, AB, OO. Blood type alleles A and B are codominant. O is recessive to both A and B.

-Example: Rh factor is determined by additional genes. Rh (+) is dominant over Rh (-). Rh (+) codes for the presence of proteins on the surface of your red blood cells. Rh (-) means you don’t have these proteins.

Polygenic

a single trait determined by the interaction between alleles of more than one gene, show continuous variation

-Ex: human height, determined by many genes that interact with your environment

Continuous variation

range of variable phenotypes rather than discrete categories

Epigenetics

our environment can influence which genes are expressed. Methylation is a process that tends to decrease gene expression. Methylation is the attachment of -CH₃ groups to DNA.

Why does the risk of having a baby with Down syndrome increase as a woman ages?

A woman’s eggs begin forming while she is still a fetus. As her eggs age, the change that her chromosomes will separate abnormally increase, leading to a higher rate of down syndrome.

Down syndrome or Trisomy 21

an individual has an extra copy of chromosome 21.

Aneuploidy

when offspring have more or fewer chromosomes than the parents. Similar to trisomy 21, is caused by nondisjunction of chromosomes during meiosis.

Nondisjunction

is when chromosomes separate unequally. Gametes can end up with either extra or fewer chromosomes.

Amniocentesis

removes fluid surrounding the fetus to obtain and analyze fetal cells to diagnose genetic disorders.

MRSA (Methicillin-Resistant Staphylococcus aureus)

infectious bacterium, difficult to treat with antibiotics, killed 10,000 people in the US in 2012. Transfers from person to person by direct or indirect contact. Athletes have increased risk of skin infections because of contact with skin, items, or surfaces that harbor MRSA.

Antibiotics

interfere with the function of essential bacterial cell structures. Beta-lactams (penicillin family) work by interfering with a bacterium’s ability to synthesize cell walls.

Binary Fission

one parental cell divides into two daughter cells. Binary fission occurs quickly, but each time it causes some changes to DNA.

Antibiotics resistance

-Random mutations can create new alleles that cause some bacteria to be resistant to antibiotics

- Gene transfer can spread alleles for antibiotic resistance to other bacteria.

Population

a group of organisms of the same species living together in the same geographic area. An entire population can change (evolve) when some traits are favored over others.

-Ex: drug resistant trait

How populations evolve

-Genetically diverse population

-Varying allele frequency

-The environment favors some alleles over others

-Allele frequency changes over time (called evolution).

Evolution

change in allele frequency over time

Fitness

organisms’ ability to survive and reproduce in a particular environment. Higher fitness= increased likelihood of alleles being passed to the next generation

Genotype determines phenotype

environment determines the success of a phenotype. Successful phenotypes become more common in the population. Change in phenotype frequency = change in genotype frequency = evolution

Natural selection

differential survival and reproduction of individuals within a population in response to environment. Advantageous traits become more common, and the population becomes better suited, or adapted, to environment.

Populations, not individuals, evolve.

Populations experience changes in allele frequencies over time.

Directional selection

predominant phenotype shifts on a particular direction. Directional selection occurs when a phenotype at one extreme is favored by the environment.

Stabilizing selection

phenotype of population settles near middle or range. Intermediate phenotypes are better suited to the environment than individuals at either extreme.

Diversifying selection

phenotype of population is at both extremes of range. Extreme phenotypes are better suited to the environment than individuals with intermediate phenotypes.

Natural Selection in Bacteria

Antibiotics change the environment in which bacteria live. When antibiotics are present, bacteria with genes for resistance have the greatest fitness. This creates strong directional selection for antibiotic resistance.

Population Genetics

study of the genetic makeup of populations and how genetic composition changes. Understand how a group of organism’s copes with environmental changes.

Gene pool

total collection of alleles in a population. Scientist can use DNA sequences to study alleles in the gene pool

Changes in allele frequency over time

evolution of populations is caused by this. Changes in alleles can be positive, negative, or neutral for fitness. This can result in the population becoming more adapted to its enviornment.

Natural selection

population is better adapted

Nonadaptive evolution

random changes that do not affect fitness for an environment. Caused by mutation, genetic drive, and gene flow. Can happen through genetic drift (change in allele frequencies between generations that occurs purely by chance, subset of population reproduces, subset of alleles represented in next generations, can decrease but not increase genetic diversity of a population)

Genetic drift

random changes in the allele frequencies of a population between generations. The smaller the population, the greater the effect of genetic drift.

Founders effect

a type of genetic drift in which a small number of individuals leaves one population and establishes a new one.

Bottleneck effect

a type of genetic drift that occurs when a population is suddenly reduced to a small number of individuals

Genetic Diversity Importance

a diverse gene pool gives a population more flexibility to survive in a changing environment. The more genetically diverse a population, the more ways it has to adapt.

Gene flow

movement of alleles from one population to another

Inbreeding

Mating between closely related individuals. Doesn’t change the allele frequency within a population. Increases the proportion of homozygous individuals to heterozygotes.

Inbreeding Depression

Closely related individuals are more likely to share the same alleles. Negative reproductive consequences for a population. Associated with high frequency of homozygotes individuals possessing harmful recessive alleles.

Hardy-Weinberg equilibrium

In a nonevolving population, allele and genotype frequencies do not change over time. This is used to identify genes that have changed because of evolutionary mechanisms.

Five necessary conditions:

-No mutation creating new alleles

-No natural selection favoring some alleles over others

-An infinitely large population size (and, therefore, no genetic drift)

-No influx of alleles from neighboring populations ( i.e., no gene flow)

-Random mating of individuals

Species

a kind of living thing. Different species concepts can be used to define what a species is. The biological species concept is the most frequently used species concept.

Biological Species Concept

A population of individuals whose members can interbreed and produce fertile offspring. Different species cannot mate because they are reproductively isolated.

Isolation types

Reproductive isolation

-ecological isolation

-temporal isolation

-behavioral isolation

-mechanical isolation

-gametic isolation

-hybrid inviability

-hybrid infertility

Speciation

genetic divergence of populations, leading over time to reproduce isolation and the formation of new species

Paleontologists

scientists who study ancient life by means of the fossil record

Fossil

the preserved remains or impressions of once-living organisms

Fossil record

an assemblage of fossils arranged in order of age, which provides evidence of changes in species over time

Tiktaalik

fossil remains discovered by research of the transition between fish and land-dwelling animals. Possessed many features of a lobe-finned fish. Also had a jointed elbow, wrist, and fingerlike bones.

Vertebrates

animals with bony or cartilaginous backbones, important part of evolution

Descent with modification (evolution)

all living things are related. Different species emerged over time due to natural selection.

Reading the fossil record

not all organisms are preserved. The fossil record is not a complete record of past life. The fossil record is extensive enough to show the arc of life.

Dating fossils

Fossils are at least as old as the rocks that encase them. Some types of rocks can be dated directly, or they can be dated relative to surrounding rocks.

Radiometric dating

use of radioactive isotopes as a measure for determining the age of a rock or fossil

Relative dating

determining the age of a fossil from its position relative to: layers of rock and fossils of known age

Invertebrates

animals without a backbone

Living on land

requires different features

-sturdier structure

-prevention of water loss

-a different way to take in oxygen

-limbs are common

Tetrapods

Vertebrate with four true limbs. Jointed, bony appendages with digits. All tetrapods share the same forelimb bones, which are arranged in the same order

Homology

similarity due to common ancestry. Also seen in early development. Similar embryological structures exist.

Homologous structures

those that are similar because they are inherited from the same ancestor. Changes to similar embryological structure take place as the organisms develop. These structures are homologous, and are evidence that vertebrates shared a common ancestor.

Vestigial Structure

inherited from an ancestor and no longer serves a clear function in the organism that possesses it. For example, a snake embryo has limb buds.

Common Ancestry

the genetic code is nearly identical among all organisms. closely related organisms share DNA sequences. Closely related species have fewer DNA sequence differences than species more distantly related. Organisms that reach a brand in the family tree more recently are more closely related. Similar organisms also have more similar DNA. DNA can be used to determine how species are related