Bio 1 Final

What is a karyotype and how are chromosomes arranged in it?

A karyotype is a micrograph in which pairs of homologous chromosomes are arranged in decreasing size. Images are taken of chromosomes stained during metaphase arranged by size to produce the micrograph.

What information can a human karyotype provide?

A human karyotype shows chromosomes arranged in pairs based on size and shape including the sex chromosomes. It reveals banded structures indicating DNA density regions and is used to identify chromosomal abnormalities and genetic disorders.

What are telomeres and what roles do they play in chromosomes?

Telomeres are protective caps on chromosomes made of DNA associated with proteins. They serve to protect the chromosome structure and recent evidence suggests they might be involved in aging and cancer processes.

Define nondisjunction and when it can occur during cell division.

Nondisjunction is the failure of sister chromatids to properly separate during cell division occurring during meiosis I or II. This results in gametes with abnormal numbers of chromosomes.

What are the consequences of nondisjunction during meiosis for the offspring?

When gametes with abnormal chromosome numbers from nondisjunction combine during fertilization the resulting offspring may have an incorrect number of chromosomes leading to genetic disorders such as Down syndrome.

What is Down syndrome and how is it related to nondisjunction?

Down syndrome is a human chromosomal disorder caused by trisomy 21 where three copies of chromosome 21 are present due to nondisjunction. Its frequency increases with maternal age.

Describe what is observed in a karyotype of an individual with Down syndrome.

The karyotype shows 23 pairs of chromosomes with an extra copy of chromosome 21 (trisomy 21) clearly visible and often circled. The chromosomes are numbered 1 to 22 plus the sex chromosomes.

Can nondisjunction affect sex chromosomes as well as autosomes?

Yes nondisjunction can occur in both autosomes and sex chromosomes potentially leading to disorders involving sex chromosome abnormalities.

Explain incomplete dominance using the example of flower color.

Incomplete dominance occurs when the heterozygous phenotype is intermediate between the two homozygous phenotypes. For example crossing a red flower (RR) with a white flower (rr) produces pink flowers (Rr); self-fertilizing pink flowers produces offspring with a phenotype ratio of 1 red : 2 pink : 1 white.

How does the phenotype ratio 1:2:1 in incomplete dominance correspond to the genotypes?

In incomplete dominance the 1:2:1 phenotype ratio corresponds to 1 homozygous dominant (RR) 2 heterozygous (Rr) and 1 homozygous recessive (rr) individuals exhibiting red pink and white flowers respectively.

What is codominance and how does it differ from incomplete dominance?

Codominance is a genetic situation where both alleles in a heterozygous individual are fully expressed unlike incomplete dominance where the heterozygote shows an intermediate phenotype. In codominance both traits appear simultaneously.

What causes red blood cells to change shape in sickle-cell disease?

Changes in hemoglobin cause red blood cells to change to a sickle shape.

What is the characteristic of individuals heterozygous for the sickle-cell trait?

They have both normal and sickle-shaped red blood cells.

What are the three forms of alleles in the ABO blood group system?

The alleles are I^A I^B and i.

How do the alleles I^A and I^B interact in the ABO blood group inheritance?

I^A and I^B alleles show codominance resulting in blood type AB when both are present.

What blood type results from the genotype ii in ABO blood groups?

Blood type O results from the genotype ii.

What does it mean when an inheritance pattern involves multiple alleles?

It means more than two alternative forms (alleles) of a gene exist in the population but each individual still carries only two alleles.

What is the hierarchy of dominance among the four alleles controlling rabbit coat color?

The alleles are C c^ch c^h and c which demonstrate a hierarchy of dominance influencing coat color.

What is epistasis in genetics?

Epistasis is when one allele hides or masks the effects of another allele affecting the phenotype.

How does epistasis affect Labrador retriever coat color?

Certain alleles (like 'e') can prevent dark pigment from being present in the fur hiding the effects of other coat color alleles.

In Labrador retrievers what coat color results from the genotype eebb?

A light yellow coat color with no dark pigment present in the fur.

What chromosomes determine an individual's gender?

Sex chromosomes determine gender typically the X and Y chromosomes.

Explain the outcomes of sex determination using the XY chromosome system.

An egg (X) fertilized by a sperm carrying X results in XX (female) and fertilization by a sperm carrying Y results in XY (male). The probability of each is roughly 50%.

What is dosage compensation and why is it important?

Dosage compensation balances the expression of genes on the X chromosome between males (XY) and females (XX) to ensure that gene expression levels are similar despite the difference in X chromosome number.

What is a Barr body?

A Barr body is an inactivated X chromosome in female cells helping achieve dosage compensation.

What are sex-linked traits?

Traits caused by genes located on the X chromosome.

Give two examples of sex-linked traits.

Red-green color blindness and hemophilia.

What are polygenic traits?

Traits controlled by the interaction of multiple pairs of genes resulting in continuous variation in the phenotype.

How does polygenic inheritance affect skin color?

Skin color results from multiple genes each adding to the amount of pigment and the combined effects form a range or gradient of pigmentation.

How does the number of dominant alleles influence polygenic traits like skin color?

Having more dominant alleles typically leads to a stronger expression of the trait for example darker skin color.

What environmental factors can influence traits?

Diet exercise sunlight exposure water availability and temperature can influence traits.

Why do environmental influences matter in genetics?

Because they can affect how genes are expressed leading to variation in phenotypes even among individuals with similar genotypes.

What is the purpose of twin studies in genetics?

Twin studies help scientists separate genetic contributions from environmental contributions by comparing traits in identical twins.

If a trait appears frequently in identical twins what does this suggest about the trait?

It suggests that the trait is at least partially controlled by heredity.

What does it indicate if traits are expressed differently in identical twins?

Traits expressed differently in identical twins are strongly influenced by environmental factors.

What type of genetic disorder expresses a trait only when an individual is homozygous recessive?

A recessive genetic disorder.

Who was Archibald Garrod and what was his contribution to genetics?

Archibald Garrod was an English physician who studied the enzyme deficiency alkaptonuria and discovered that such disorders run in families.

What is a carrier in terms of recessive genetic disorders?

An individual who is heterozygous for a recessive disorder is called a carrier; they carry the recessive allele but typically do not express the disorder.

What causes cystic fibrosis at the genetic level?

Cystic fibrosis is caused by a defective gene that codes for a membrane protein involved in chloride ion transport.

How does cystic fibrosis affect the body?

It causes excessive mucus production leading to digestive and respiratory failure because chloride ions are not absorbed properly into cells.

Why does cystic fibrosis result in thick mucus secretions?

Because insufficient chloride ions enter the cells causing water to be retained outside the cells and resulting in thick sticky mucus.

Is there a cure for cystic fibrosis? If not what treatments exist?

There is no cure; treatments include daily clearing of mucus from the lungs mucus-thinning drugs and pancreatic enzyme supplements.

What is albinism and what gene effect causes it?

Albinism is a genetic disorder caused by altered genes that result in the absence or very low production of the pigment melanin in skin hair and eyes.

Describe the physical characteristics of an individual with albinism.

They have white hair very pale skin and pink pupils due to lack of pigment.

How does albinism affect the individual's health besides appearance?

Their skin is highly susceptible to UV damage and they often have vision problems.

How common is albinism in the U.S.?

About 1 in 17000 individuals.

What causes galactosemia and what are its effects?

Galactosemia is caused by the absence of the gene that codes for the enzyme needed to break down galactose leading to mental disabilities an enlarged liver and kidney failure.

What is the treatment for galactosemia?

There is no cure; treatment involves restricting lactose and galactose in the diet.

What is Tay-Sachs disease caused by genetically?

It is caused by the absence of a necessary enzyme that breaks down fatty substances called gangliosides.

What happens in the brain as a result of Tay-Sachs disease?

Gangliosides accumulate in the brain inflating brain nerve cells and causing mental deterioration.

What is the typical prognosis for someone with Tay-Sachs disease?

There is no cure or treatment; the disease usually leads to death by age 5.

How does cystic fibrosis affect chloride ion movement in the body?

Chloride ions are not absorbed into the cells but rather are excreted in the sweat disrupting the ionic balance and leading to thick mucus secretion.

Explain the role of enzymes in recessive genetic disorders illustrated by Archibald Garrod's research.

Enzyme deficiencies such as those studied by Garrod in alkaptonuria can cause inherited disorders because the absence or malfunction of an enzyme disrupts normal metabolism.

Why is the study of identical twins critical for understanding complex inheritance patterns?

Because identical twins share the same genetic makeup differences in trait expression can highlight the influence of environmental factors separate from genetics.

What is galactosemia and how does it affect the body?

Galactosemia is a recessive genetic disorder characterized by the body's inability to digest galactose. If a galactosemic infant consumes milk unmetabolized milk sugars build up and damage the liver eyes kidneys and brain causing symptoms like brain damage cataracts jaundice enlarged liver and kidney damage.

How do recessive genetic disorders differ from dominant genetic disorders in terms of inheritance?

Recessive disorders require both parents to carry the allele for the disorder while dominant disorders only need one parent to have the allele to pass the trait. Additionally dominant disorders have no carriers—individuals either have the disorder or do not.

Name two examples of dominant genetic disorders mentioned and describe their effects.

Huntington's disease affects the nervous system causing a decline in mental and neurological functions and deterioration of the ability to move. Achondroplasia is a genetic condition causing small body size and short limbs along with a large head.

Why is there a higher frequency of recessive disorders in populations compared to dominant disorders?

Because recessive disorders require two copies of the defective allele and carriers do not show symptoms these alleles can be passed silently through populations. Dominant disorders manifest even if only one allele is present which often limits their frequency.

What information does a pedigree provide in genetic studies?

A pedigree is a diagram that traces the inheritance of a particular trait through several generations. It helps visualize which individuals express carry or lack the trait and shows familial relationships such as parents and siblings.

What do the symbols in a pedigree chart typically represent?

In pedigrees yellow circles represent normal females dark red circles females expressing the trait and yellow circles half-filled with dark red represent carrier females. Similarly yellow squares denote normal males dark red squares males expressing the trait and yellow squares half-filled with dark red indicate carrier males. Lines reflect relationships and generations.

How can pedigrees be used to infer genotypes?

By observing which individuals express or carry traits across generations scientists can use pedigree patterns to determine likely genotypes—whether individuals are homozygous heterozygous or unaffected for certain genetic traits.

What role does record keeping play in predicting genetic disorders?

Accurate record keeping of family trait inheritance through pedigrees allows scientists to study inheritance patterns determine phenotypes and infer genotypes which helps predict the risk of genetic disorders in families.

Who is Gregor Mendel and why is he significant in genetics?

Gregor Mendel was an Austrian monk who published findings in 1866 on inheritance patterns by breeding pea plants. He is known as the "Father of Genetics" for discovering fundamental laws of heredity through his experiments.

What is inheritance (heredity) in genetics?

Inheritance or heredity is the passing of traits from one generation to the next explaining how offspring receive genetic information from their parents.

Describe Mendel's method in studying genetic inheritance.

Mendel performed cross-pollination of pea plants carefully breeding plants with specific traits and observing how those traits appeared in subsequent generations to understand inheritance patterns.

What is the parental generation in Mendelian genetics also called?

The parental generation is also known as the P generation.

What is the first filial generation (F₁) in Mendelian genetics?

The first filial generation (F₁) is the offspring resulting from a cross of the parental (P) generation.

What defines the second filial generation (F₂) in Mendelian genetics?

The second filial generation (F₂) is the offspring produced by crossing or self-fertilizing individuals from the F₁ generation.

What trait ratio did Mendel observe in the F₂ generation of pea plants for seed color?

Mendel observed a 3:1 ratio of yellow to green peas in the F₂ generation (6022 yellow peas to 2001 green peas).

List the seven different traits Mendel studied in pea plants.

Mendel studied seed or pea color flower color seed pod color seed shape or texture seed pod shape stem length and flower position.

What is an allele?

An allele is an alternative form of a single gene passed from generation to generation.

What does it mean when an allele is dominant?

A dominant allele is one that determines the phenotype when at least one copy is present; it masks the effect of a recessive allele.

What does it mean when an allele is recessive?

A recessive allele is one whose trait is masked in a heterozygous organism and only expressed if two copies of it are present.

What does homozygous mean in terms of alleles?

An organism is homozygous when it has two identical alleles for a particular trait.

What does heterozygous mean regarding alleles?

An organism is heterozygous when it has two different alleles for a particular trait.

Define genotype.

Genotype refers to an organism's allele pairs the genetic makeup for a particular trait.

Define phenotype.

Phenotype is the observable characteristic or outward expression of an allele pair.

Summarize Mendel's Law of Segregation.

Mendel's Law of Segregation states that two alleles for each trait separate during meiosis and during fertilization two alleles unite. Heterozygous organisms are called hybrids.

What is a hybrid in genetics?

A hybrid is a heterozygous organism having two different alleles for a particular trait.

In Mendel's experiments with pea plants what is the genotype and phenotype of the F₁ hybrid for seed color?

The F₁ hybrid has the genotype Yy (heterozygous) and the phenotype is yellow seed color as yellow is dominant over green.

What is a monohybrid cross?

A monohybrid cross is a cross that involves hybrids (heterozygous individuals) for a single trait.

Explain what happens during self-fertilization in the F₁ generation in Mendel's pea plant experiments.

During self-fertilization F₁ hybrid plants (Yy) produce gametes that combine randomly resulting in F₂ offspring with genotypes YY Yy and yy producing the 3:1 phenotypic ratio.

What is a dihybrid cross?

A dihybrid cross is the simultaneous inheritance of two or more traits involving individuals heterozygous for both traits.

Define Mendel's Law of Independent Assortment.

Mendel's Law of Independent Assortment states that genes on separate chromosomes sort independently during meiosis so random distribution of alleles occurs and each allele combination is equally likely.

Why is the 3:1 ratio important in understanding Mendelian genetics?

The 3:1 ratio observed in the F₂ generation provides evidence for the segregation of dominant and recessive alleles and how traits are inherited predictably.

What is a Punnett square and what is it used for in genetics?

A Punnett square is a tool used to predict the possible genotypes and phenotypes of offspring resulting from a cross between parents with known genotypes.

In a Punnett square involving two heterozygous parents (Tt) what are the possible genotypes and their proportions for the offspring?

The possible genotypes are TT Tt Tt and tt which corresponds to a genotype ratio of 1 TT : 2 Tt : 1 tt.

What do the alleles 'T' and 't' represent in the tongue rolling Punnett square example?

'T' represents the ability to roll the tongue and 't' represents the inability to roll the tongue.

What is a dihybrid cross and what typical phenotypic ratio results from such a cross?

A dihybrid cross involves two traits each with two alleles. The typical phenotypic ratio from a dihybrid cross is 9:3:3:1.

In a dihybrid cross of pea plants with seed color (yellow or green) and seed shape (round or wrinkled) what does the phenotypic ratio 9:3:3:1 represent?

It represents 9 yellow round seeds 3 green round seeds 3 yellow wrinkled seeds and 1 green wrinkled seed indicating the distribution of phenotypes in the F2 generation.

How many possible gamete types are produced by a dihybrid parent and why?

Four types of gametes are produced because each parent has two genes with two alleles each; independently assorted this leads to four allele combinations.

Define genetic recombination and explain how it occurs.

Genetic recombination is the production of new combinations of genes due to crossing over during meiosis and independent assortment of chromosomes.

How can you calculate the number of gene combinations produced by independent assortment?

The number of gene combinations can be calculated using the formula 2ⁿ where n is the number of chromosome pairs.

What is gene linkage and how does it relate to Mendel's law of independent assortment?

Gene linkage refers to genes located close together on the same chromosome that tend to be inherited together which means they usually do not segregate independently creating an exception to Mendel's law of independent assortment.

Describe the final product of meiosis in a case of gene linkage with alleles A B and a b.

The four gametes produced contain parental combinations of alleles either AB or ab showing that linked genes tend to be inherited together rather than assorting independently.

What is polyploidy?

Polyploidy is the condition where an organism has one or more extra complete sets of chromosomes beyond the normal diploid number.

What does a triploid organism (3n) mean?

A triploid organism has three complete sets of chromosomes instead of the usual two sets found in diploid cells.

How many chromosomes do humans have and what are homologous chromosomes?

Humans have 46 chromosomes arranged in 23 pairs. Homologous chromosomes are pairs of chromosomes one from each parent that carry genes for the same traits.

Explain the process of chromosome replication and formation of homologous chromosomes.

During replication each chromosome duplicates to form two sister chromatids joined at a centromere. Two homologous chromosomes each consisting of sister chromatids come together to form a pair.

What is a haploid cell?

A haploid cell contains a single set of chromosomes (n) which is half the number of chromosomes of diploid cells. Gametes are haploid cells.