IB - Bio chapter 3 section 2

Describe the characteristics of stem cells that make them potentially useful in medicine.

(stem cells) have/retain the capacity to divide; can be used to produce cell cultures/large number of identical cells; can be used to repair/replace damaged/lost cells/tissue;(stem cells) are undifferentiated / have not yet differentiated/specialized; can differentiate/specialize in different ways / are pluripotent/totipotent; can be used to form a variety of different tissues / form organs;used in medical research; used in treatment of (named) disease;

Which of the following statements about homologous chromosomes is correct? A. Each gene is at the same locus on both chromosomes. B. They are two identical copies of a parent chromosome which are attached to one another at the centromere. C. They always produce identical phenotypes. D. They are chromosomes that have identical genes and alleles.

A. Each gene is at the same locus on both chromosomes.

Which genetic condition can be diagnosed by karyotyping? A. Trisomy 21 B. Sickle-cell anemia C. Hemophilia D. Colour blindness

A. Trisomy 21

What causes the presence of three chromosomes 21 in Down syndrome? A. Crossing over B. Allele change C. Non-disjunction D. Gene mutation

C. Non-disjunction

What is a possible source of the chromosomes used for pre-natal karyotype diagnosis? A. The mother's lymphocytes B. The mother's cheek cells C. The cells from chorionic villi D. The fetal hair root cells

C. The cells from chorionic villi

Which is a source of chromosomes for pre-natal diagnosis of abnormalities by karyotyping? A. Sperm B. Ovaries C. Erythrocytes D. Chorionic villi

D. Chorionic villi

Distinguish between autosomes and sex chromosomes in humans.

X and Y chromosomes determine sex; females XX and males XY;X chromosome is larger than / carries more genes than the Y chromosome;22 types/pairs of autosomes; males and females have same types of autosomes;

Discuss whether or not horses and donkeys should be placed in the same species.

a. to be in same species two organisms must have the same genes arranged on the same chromosomes OR must have the same number of chromosomes

State the technique used to collect cells for pre-natal testing.

amniocentesis/sampling amniotic liquid/fluid (via needle)/chorionic villus sampling

Define the terms chromosome, gene, allele and genome.

chromosome: structure formed by DNA and proteins; gene: a heritable factor that controls a specific characteristic; allele: one specific form of a gene occupying the same gene locus as other alleles of the gene; genome: the whole of the genetic information of an organism;

Deduce the reason for the person developing as a female.

no Y chromosome.

Outline a technique of gene transfer resulting in genetically modified organisms

gene transfer takes a gene from one species/organism and inserts it into another; using plasmid/viral vector/ballistic impregnation/electroporation; use of reverse transcriptase to obtain gene from mRNA; restriction enzyme/endonuclease used to cut out/excise gene;(same) restriction enzyme used to cut open plasmid; sticky ends used to link DNA/link gene to plasmid; DNA ligase used to seal nicks/splice; bacterium takes in plasmid / plasmid transferred to bacterium/plant/host cell; valid documented example (e.g. human insulin from bacterium/yeast / salt-tolerant tomato plant / carotene/vitamin A in rice /herbicide/Roundup/glyphosate resistance in crop plants / factor IX/clotting factor in sheep milk / low phosphate feces in pigs;

Which is a characteristic of the pairs of sister chromatids that are visible during meiosis? A. They result from the replication of DNA before meiosis. B. They are only present in meiosis I. C. They split apart during metaphase I in meiosis. D. They are only present in meiosis II.

A. They result from the replication of DNA before meiosis.

What is a characteristic of the human Y chromosome? A. It is made of DNA and histones covered by phospholipids. B. It contains some genes that are not present on the X chromosome C. It is the largest chromosome in the human karyotype. D. It has a condensed length of approximately 100 µm.

B. It contains some genes that are not present on the X chromosome

Which is a characteristic of the haploid number of eukaryotic chromosomes? A. It doubles in mitosis. B. It is fixed for each species. C. It is an even number for all species. D. It is positively correlated with an animal's mass.

B. It is fixed for each species.

The diploid number of chromosomes in humans (Homo sapiens) is 46 and the diploid number of chromosomes in rice (Oryza sativa) is 24. What does this indicate about diploid chromosome numbers? A. Plant species have a lower diploid number of chromosomes than animals. B. Members of a species have the same diploid number of chromosomes. C. The evolutionary progress of species is determined by the diploid number of chromosomes. D. The complexity of the organisms is correlated to the diploid number of chromosomes.

B. Members of a species have the same diploid number of chromosomes.

What is characteristic of homologous chromosomes? A. They have an identical DNA sequence. B. They are of the same length in karyograms. C. They form pairs in prokaryotes. D. They carry the same alleles.

B. They are of the same length in karyograms.

What is the composition of eukaryotic chromosomes? A. DNA only B. DNA and ribose C. DNA and RNA D. DNA and proteins

D. DNA and proteins

Explain the use of karyotyping in human genetics.

Definition and construction of karyotypes:karyotype is the number and type / image of chromosomes in a cell; cells collected from chorionic villus / by amniocentesis; requires cells in metaphase / stimulate cells to divide and reach metaphase; burst cells and spread chromosomes / photo taken of chromosomes; chromosomes are arranged in pairs; according to size/structure/position of centromere/banding pattern; Uses for karyotypes:karyotypes used to identify sex/gender; male is XY and female XX; used to identify chromosome mutations/abnormal numbers/non-disjunction;Down syndrome due to extra chromosome 21 / other trisomy/aneuploidy example; used for pre-natal diagnosis of chromosome abnormalities; may lead to a decision to abort the fetus; prepare for consequences of abnormality in offspring;

Describe the causes of Down syndrome.

Down syndrome is caused by non-disjunction; occurs during meiosis; chromosome pairs fail to separate in meiosis I / chromatids in meiosis II / anaphase II; some gametes have an extra chromosome; can lead to zygotes/individuals with an extra chromosome / individual has 47 chromosomes; in Down syndrome this would be trisomy 21/extra chromosome 21; increased probability with increased age of mother/ages of parents;

describe ABO blood groups as an example of co dominance.

allele IA and the allele IB are (co)dominant as they are both expressed in the heterozygote/AB type blood / OWTTE

State the method used to arrange the chromosomes in a karyotype.

chromosomes are grouped by pairs according to size and structure/band pattern/location of centromeres

Describe the role of sex chromosomes in the control of gender and inheritance of hemophilia.

two sex chromosomes are X and Y; one sex chromosome inherited from each parent;XX results in female;XY results in male; sex determined by sperm/father; sex-linked genes are those located on the sex chromosomes / usually refers to genes on X chromosome; recessive sex-linked traits appear more frequently in males since they only have one X chromosome; hemophilia is an example of a gene located on the X chromosome/sex-linked; female carriers are heterozygous / XHXh; males with hemophilia are XhY / normal males are XHY; sons (of carrier females) have 50 % probability of showing the trait (even if father is normal);daughters (XhXh) of hemophiliac father and carrier mother can be affected / daughters who receive an affected X from each parent will have hemophilia;The points above can be gained by annotated Punnett squares.Candidates may introduce a lettering system for haemophilia genotypes which does not include H and h. Accept other letters for superscripts, but same alphabetical letter should be used throughout, dominant form should appear as upper case letter and recessive as lower case letter.